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Geology is all around us, scarcely thought of as we go about our lives. Yet, it affects everything we do as a civilization, as a society and as individuals. While barely appearing to change from day to day, it works to alter the course of evolution. Preserving a record of creatures and landscapes both ancient and forgotten, the story of our past is written in stone and waiting to be read. I offer a view of how I see our world and its inhabitants, both past and present, as seen through my lens.
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    Vox Clamantis In Deserto
    "The voice of one crying out in the wilderness"

    From the Dartmouth College motto adapted from the Gospel of Mark and
    subtitle of Merle Graffam's treatise entitled Fossils from the Tropic Shale

    Although some dinosaurs may have spent time feeding in open water and possibly a few may have become strongly amphibious as implied by some trackways, it’s a common misconception that dinosaurs colonized the seas. If so, what were the bones of a terrestrial dinosaur – a new species of therizinosaur - doing amongst the marine fauna of the Late Cretaceous Tropic Shale, at least 60 miles from the nearest dry land at the time?

    Artist Victor Leshyk’s portrayal of the proto-feathered, Late Cretaceous dinosaur Nothronychus graffami dining upon mangroves growing marginal to the Western Interior Seaway. The therizinosaur is thought capable of balancing tripodally on its massive pelvis while raking in tree branches with its long slender claws, which it passed to its toothless beak.
    From the Museum of Northern Arizona. Visit Victor here. Visit MNA here.


    If you’ve ever visited the badlands outside of the tiny southern Utah town of Big Water, you know the meaning of the word “barren”. The landscape consists of a coarse, brownish sandstone bedrock covered by a monotonous repetition of eroding, low-slung, blue-gray mounds of fine mud turned-to-shale against a backdrop of buff-colored, sandstone cliffs littered at the base with dislodged blocks of stone. Little grows and nothing moves, other than the wind and the imperceptible forces of gravity and erosion that are incessantly at work.  

    The region is so drab and desolate that locals call it ‘The Moon.’ To geologists and paleontologists – who are of the same ilk - it’s all hauntingly beautiful and exciting beyond anything imaginable, not just for its appearance but for the story of its formation and the bounty of lifeforms that are preserved. Personally, I couldn’t wait to get out there with geologist and acclaimed author Wayne Ranney, and Merle Graffam - namesake of the dinosaur Nothronychus graffami.

    Indeed, there’s nary a sole in sight on The Moon unless you stumble upon Merle - retired commercial artist, Big Water resident, Bureau of Land Management Park Ranger at the Big Water Visitor Center, and amateur paleontologist par excellence. Merle takes regular walks on the Moon, combing the ancient seabed for marine fossils with the intuition, trained eye, laser focus and insatiable curiosity of a seasoned field expert. 


    Merle knows The Moon and the fossils preserved within in it, all creatures of a long gone sea - megafaunal marine and brackish-water invertebrates such as oysters, gastropods, solitary corals, inoceramid bivalves and ammonites, and marine vertebrates such as fish, rays and sharks, turtles, crocodilians and an occasional short-necked plesiosaur. Above the sea soared pterosaurs and early avians with toothed-beaks. As bleak and depauperate as the landscape looks now, at one time, The Moon was the site of a thriving marine ecosystem. 

    Creatures above and within the Late Cretaceous Western Interior Seaway
    Adapted from

    Terrestrial deposits marginal to the sea preserve extensive skeletal remains and trackways that attest to a diverse dinosaur fauna that plied the shoreline's habitats, while diminutive, insectivorous mammals hid in the shadows amongst the gymnosperms and newly-evolved angiosperm plants. It takes considerable imagination to view this ancient land and seascape while standing on the landscape of The Moon.

    The lowland-sea interface of The Moon in the Late Cretaceous consisted of many paleoenvironments - habitats that supported a rich array of lifeforms. Seaward, deeper muds led to sandy shores and various sea grasses. Mixed salinity-plants such as mangroves thrived nearshore and onshore, possibly the haunt of therizinosaurs. Further inland, larger trees such as cypress and hardwoods thrived.
    Modified from Plateau Magazine, 2007. 

    On one of Merle's lunar constitutionals in 2000, he made an unsuspecting discovery that would change his life. What's more, it would rewrite a portion of dinosaur phylogeny, offer a new perception of dietary plasticity amongst theropods and expand our knowledge of biodiversity within the Cretaceous ecosystem.

    Merle discovered a small toe-bone - a phalange - in the Tropic Shale that eventually would lead to the remains of a spectacular dinosaur skeleton at the crest of a small hillock of eroding marine sediments of the Tropic Shale. It proved to be the most complete therizinosaurid yet discovered in North America.

    Very excited at the excavation site, Merle exclaimed, "Here's the spot!"


    With a population barely of 475, the settlement of Big Water is a tiny speck on the map (green laser dot) located in Kane County on Highway 89 in southernmost Utah near the Arizona border. On maps from the late 50’s and early 60’s, it's called Glen Canyon City and housed workers who built the nearby Glen Canyon Dam.

    The name Big Water seems a misnomer, since the high desert and badlands are as dry as a bone with an average rainfall of barely six inches a year. The nearest “big water” is a slender arm of Lake Powell called Wahweap Bay about 10 miles down the highway to the southeast, where a trip downstream leads to the dam that impounds the Colorado River. So where’s all the water at Big Water?

    Wayne Ranney aims his laser-pointer at Big Water on a topographical relief map at the Big Water Visitor Center. The highway takes you down and across the Glen Canyon Dam that impounds Lake Powell. 

    Big Water is actually named for the Navajo Aquifer, an underground formation with an estimated 400 million acre-feet of potable water that spans most of southwestern Utah and some of northern Arizona. Yet geologically, the name is highly appropriate, since a much earlier actual “big water” submerged the entire region and a wide swath of North America during the Late Cretaceous. That sea was responsible for the layered deposits at the Moon of Big Water – and as we shall see - much more. 
    Panorama from Scenic Byway 89 looking northeast from Big Water.
    The eroded, gray badlands at the cliff-base are composed of Tropic Shale, while the cliffs are of composed of resistant Straight Cliffs Sandstone. Beneath the Tropic is the Dakota Sandstone. The high desert's sand is a Quaternary mix of unconsolidated surficial deposits. Click on the photo for a larger view.
    Big Water is just outside the Kaiparowits Plateau section of the Grand Staircase-Escalante National Monument in south-central Utah, which in turn is on the western margin of the Colorado Plateau - an arid region of high relief centered over the four corners region of Utah, Arizona, Colorado and New Mexico. President Bill Clinton controversially designated the region a national monument in 1966 - an area rich in geology, paleontology and human history.

    The three sections of the Monument record sedimentation throughout the Mesozoic. The centrally-located Kaiparowits Plateau section is exemplified by plateaus, buttes and mesas carved in rocks acquired in the Cretaceous when the region was situated along the western shore of an extensive inland body of shallow water called the Western Interior Seaway.

    Three sections of the Grand Staircase-Escalante National Monument in southern Utah with Big Water on Highway 89 near the Arizona border.
    Modified from Utah Geological Association, Second Edition DVD.


    Today, the Monument is elevated two kilometers along with that of the Colorado Plateau, but throughout the Paleozoic much of western Laurentia (the cratonic core of the supercontinent of Pangaea) was situated at sea level. Beginning in the latest Proterozoic and throughout most of the ensuing Paleozoic, an ocean called the Panthalassic (Paleo-Pacific) lapped onto the continent's western margin, leaving limestone deposits now deeply buried below the Monument. In the Cretaceous Period of the Mesozoic, marine waters returned as the Western Interior Seaway - only this time inland and following Pangaea's disassembly in the Mesozoic. Like the Panthalassic (that became the Pacific Ocean), the Seaway left its mark in the form of sedimentary deposits preserved on the Great Plains and the Colorado Plateau. In the Tertiary, the Colorado Plateau and the Rocky Mountains were uplifted, casting the sea from the continent's craton and stripping off much of the sea's depositional legacy from the Plateau. 
    By what geological process did the Kaiparowits section and The Moon of Big Water come to be flooded in the Cretaceous by an inland sea?
    In the Late Triassic, Pangaea began to break apart in the north-central Atlantic Ocean. As rifting progressed at the mid-ocean ridge, newly-formed North America began to drift westward, while nascent Europe, Africa and South America headed east and south, respectively. Beginning in the latest Jurassic at the west margin, a tectonic plate collision initiated between the overriding continental plate of North America and the east-directed, subducting Farallon plate of the Pacific Ocean.
    Plate convergence resulted in a mountain-building deformational event called the Sevier orogeny that extended over 1000 km eastward into the craton. The event had far reaching consequences for deposition across the continent's mid-section, particularly during the Cretaceous - with the most stratigraphically complex sequence of sedimentary rocks on the Colorado Plateau.
    North American tectonics during the Early Cretaceous (125 Ma)
    Two large arms of the rising sea are about to converge, held up temporarily by tectonic barriers such as the Trans-Continental Arch and the Ouachita Uplift. Ocean basins, inherently deeper, are designated as dark blue: whereas, shallow epicontinental (epeiric) basins and continental shelves are light blue.
    Adapted from Ron Blakey and Colorado Plateau Geosystems Inc.

    The Sevier front consisted of a fault zone, an active volcanic arc, low-angle thrust slices and a broad foreland basin. The retroarc basin - so called because it was 140-200 km cratonward of the thrust front - was an asymmetric depression created in response to the load superimposed by the east-advancing wedge of thrust sheets that downwarped the lithosphere. I
    n response to ongoing Sevier thrusting, the foreland migrated eastward and continued to rapidly subside. The basin received massive amounts of detritus delivered by rivers across alluvial plains from the encroaching front from the west and southwest.

    East-directed subduction of the Farallon plate beneath the North American plate initiated loading that drove lithospheric flexure and subsidence. The resulting accommodation space that formed preserved up to 20,000 feet of sediment and received an influx of marine waters from the north and south.
    Modified from Plate Tectonics by Frisch et al

    In the Early Cretaceous (Aptian to Albian), the basin began to flood with marine waters from the north and south, connecting the Boreal and Tethyan seas. By the Late Cretaceous, long arms of the sea converged forming an inland epicontinental sea (epi is Greek for above). Nearest the front, deep-water sediments pass upward into shallow-water sediments recorded with conglomerates that pass into sandstones and shales, which in turn pass into carbonate marine sediments well to the east.

    Late Cretaceous oblique, north view of the asymmetric Western Interior Seaway illustrating the subducting Farallon slab, the Sevier orogen and Western Interior Seaway.
    Modified from Wikipedia

    The development of the inland sea occurred by active subsidence of the foreland but was assisted at a time of eustasy (global high seas). Sea level changes are affected by the volume of water contained in the ocean basins and the volume of water displaced from the basins. For example, melting polar ice adds to the basins causing glacioeustasy, and shifting plates and shallowing basins removes water called tectonoeustasy. It's a rather simplistic scenario but not far from reality.

    Pangaea's aridity during the Triassic and Jurassic - demonstrated by widespread eolian sandstones and evaporites in the west - was replaced by a humid, subtropical climate in the Cretaceous, as North America drifted out of lower, equatorial latitudes. Concurrently, as Atlantic seafloor spreading increased, the ocean basin shallowed, displacing vast quantities of water, while extrusive continental volcanics associated with rifting elevated temperatures 18°F (10°C) higher than average.

    Submitting to the global greenhouse, melting polar ice further drove seas higher. Low-lying regions - coasts, interior lowlands and cratonic platforms - drowned worldwide including the subsiding basin of the Sevier foreland. And in its wake, the seas left vast sequences of sedimentary rocks. The great flood is known as the Zuni transgression - the greatest of six major high water events of the Phanerozoic. As an aside, our modern world with rising seas is in a state of Holocene (post-Pleistocene) glacioeustasy. Now back to the Cretaceous Seaway!

    The six major transgressions of the Phanerozoic Eon with the Cretaceous Zuni highlighted.
    Modified from Earth System History, Second Edition, 2005 and

    At its zenith in the Late Cretaceous, the Western Interior Seaway in places was almost 300 meters deep. Inland seas are built on buoyant continental platforms and are relatively shallow compared to deeper-denser ocean basins. The sea connected the Arctic Ocean and Hudson Bay with the Gulf of Mexico, and stretched from Utah in the west to the western Appalachians in the east. It split North America into two massive landmasses - eastern Appalachia and western Laramidia - and divided the terrestrial ecosystem forcing it to pursue independent courses of evolution, as did the resident faunal populations riding on Pangaea's drifting continental siblings.

    North America in the Late Cretaceous (92 Ma)
    The Western Interior Seaway (light blue and white) has flooded the foreland across the continent's mid-section, uniting the waters of the Arctic and Hudson Bay with the Gulf of Mexico, while creating two massive continental islands. Laramidia, in the far north, formed a land bridge through Beringia connecting North America and Asia. Submerged Big Water is located at the red dot. Notice coastal flooding on the subsiding shelf of all newly-formed Atlantic passive margins. Dark blue represents deep ocean basins.
    Adapted from Ron Blakey and Colorado Plateau Geosystems Inc.


    Also in the Late Cretaceous, Laramidia formed an arctic land-based connection with northeast Asia called Beringia. The loosely defined region in the vicinity of the Bering Strait has intermittently persisted through Recent times. During the Pleistocene, an Ice House climatic condition created regressive global seas exposing the land bridge; whereas during the Greenhouse conditions of the Cretaceous, the land was devoid of polar ice, having formed tectonically from a series of accretionary events. Like the Pleistocene connection that allowed the passage of Paleo-Indians and mammalian megafauna (the Asian saber-toothed cat comes to mind), the Cretaceous bridge (up to a 1,000 miles wide) likely allowed faunal and floral exchange in a similar manner in both directions.

    Approximate extent of the Beringia Land Bridge
    Adapted from

    In the Late Cretaceous, Laramidia experienced a major evolutionary radiation of dinosaurs possibly related to new biomes generated by the Sevier front and foreland, and may have been infused by immigrant fauna that migrated across the bridge from Asia (or vice-versa). The relevance of Cretaceous paleography will become relevant in our forthcoming discussion of therizinosaurs from Laurasia (the combined landmasses of North America and Eurasia that formed Pangaea with Gondwana of the Southern Hemisphere). 

    During the Late Cretaceous for nearly 25 million years, the Western Interior Seaway dominated paleography and sedimentation over a vast area of the Southwest. At least two major and numerous minor transgression-regression sequences - called cyclothems - are recorded in the rock record.

    Marine waters advanced onto the continent's downwarping interior, rising and falling with starts and stops while the shoreline shifted to and fro from east to west. As the sea advanced onto land, the sandy shore was buried by new, higher shores, while previously deeper muds migrated as well. Terrestrial deposits met marine that vied for space in an overlapping, alternating geometry, all related to the whim of the vacillating sea. When the sea eventually reversed its direction, the opposite layered architecture was deposited as newer shorelines formed on previously deeper muds called a transgressive-regressive sequence - visible stratigraphically.

    The west part of the GSENM was elevated by Sevier tectonics before sediments were deposited in coastal areas ahead of the encroaching inland sea from the east. All Upper Jurassic and a good part of Middle Jurassic rocks were removed by erosion before Cretaceous sediments were deposited.

    Generalized geologic map of the southernmost Kaiparowits section of the Monument (dotted line). The region represents a structural basin but is topographically high, having achieved its relief along with that of the Colorado Plateau. Big Water is just outside the boundary. Note the Cretaceous deposits of the Dakota, Tropic and Straight Cliffs in the region.
    Modified from of Grand Staircase-Escalante National Monument, Utah by Doelling et al, 2000.

    Initial alluvial plain and coastal plain deposits were met by the sea's rapidly-rising westward advance called the Greenhorn Cyclothem (late Cenomanian to middle Turonian). Deposited in the sea's first transgression in the early Late Cretaceous about 95 million years ago came coarse, yellow-brown beach sands of the shallow marine Dakota Formation, deposited on either the Morrison Formation (east) or the Entrada Sandstone (west). The Dakota contains a record of shallow brackish and marine water environments, lush coastal swamps and sandy expanses incised by rivers and streams emptying into the sea. 

    In deeper waters, the Dakota grades into dark, organic-rich Mancos Shale - called the Tropic Shale regionally - and consists of exceptionally fossiliferous blue-gray silts and muds formed about 93 million years ago. The type section crops out around the town of Tropic, Utah, about 50 miles to the northwest. Elsewhere in Utah, Tropic stratigraphic equivalents have been referred to the Tununk Member of the Mancos Shale, the Tropic equivalent in most of the Southwest.

    On top of the sequence with the sea retreated to the east lies the four-membered Straight Cliffs Formation, an overall regressive sequence rich in coal that followed the previous marine incursion about 85 million years ago. The sea returned again bringing with it another sequence of deposits, seen elsewhere on the Kaiparowits Plateau and in the Grays Cliffs of the Grand Staircase.

    The aforementioned lithologies are conformable and form a classic transgressive-regressive sequence that documents the greatest widespread rise in sea level of the Cretaceous recognized worldwide. In summary, the foreland basin's sedimentary infill represents a record Sevier orogen tectonics, flexural subsidence, weathering and sedimentation and eustatic sea level change.

    The dissected landscape rocks of The Moon of Big Water preserve Upper Cretaceous transgressive Dakota sandstone, shale and some coal buried beneath eroding gray Mancos muds and regressive cliff-forming Straight Cliffs sands and coals.  

    In 2000, at the conclusion of a large plesiosaur excavation in the Tropic, Merle turned to Dr. Dave Gillette - Utah's former state paleontologist and current Colbert Curator of Vertebrate Paleontology at the Museum of Northern Arizona in Flagstaff. Pulling a bone from his pocket, Merle uttered the now famous phrase "Hey Dave! What's this?" 

    Dave recognized the toe bone, but it was clearly not from a plesiosaur, the large marine reptile found with increasing frequency on the Tropic seabed thanks to Merle's keen eye of discovery. The bone was too small to be from a hadrosaur, a terrestrial, duck-bill dinosaur found in large numbers along the shoreline far to the west. 

    Stumped by the implication of a dinosaur bone so far from land, they later returned to the site, found more bones and initiated an excavation. The dinosaur's identity was a mystery well into the dig. According to Dave, “We weren’t thinking ‘therizinosaur’ at first, because at that time they were known only from Asia. From that first toe bone, we thought maybe we had a big ‘raptor’ (an agile, hunting dinosaur). But when we found peculiar bones of the massive hips, we knew we had a sickle-claw dinosaur. They were like nothing we’d ever seen.”

    The active therizinosaur excavation site in the Tropic Shale. A project can require the removal of up to 20 tons of overburden and take a thousand hours of field and laboratory time. 
    Photo by Dave Gillette

    For Merle's discovery and contribution, Graffam became the species namesake. Following the dinosaur's reconstruction, the therizinosaur was featured in an exhibit at the Museum of Northern Arizona from 2007-2009 and at the Carl Hayden Visitor Center at the Glen Canyon Dam in 2012.

    For half a century, therizinosaurs have remained a poorly known and understood group of theropod dinosaurs with an extremely unusual combination of anatomical features. That's changed largely in the last decade with new discoveries in Cretaceous deposits in Mongolia, China and western North America.

    Artist Victor Leshyk’s portrayal of the feathered dinosaur Nothronychus graffami beneath Pterandon-filled Late Cretaceous skies. Its sickle-claws are the hallmark of the family Therizinosauridae. The volcano, a ubiquitous cliché in dinosaur art, is a reminder of tectonic activity located further to the west that intermittently showered vast regions of the Southwest with datable volcanic ash.

    Unlike earlier theropod dinosaurs that exhibit predatory morphological adaptations and carnivorous inclinations, therizinosaurs exhibit the characteristics inherent of herbivores. These are thought to include: tightly-packed, leaf-shaped cheek teeth (as opposed to elongate, typically Theropod meat-cutting teeth), an inset tooth row (suggesting fleshy cheeks necessary for plant mastication) in tandem with a rostral rhampotheca (keratinous, toothless bird-like beak to facilitate an herbivorous diet), a massive, highly derived pelvis (to accommodate a large gut synonymous with plant digestion), the development of large load-bearing hind limbs (to support a large abdomen), the loss of cursorial hind-limb adaptions (typical of predatory, swift carnivorous theropods) and an increased vertebral count (long neck speculated to increase browsing range similar to sauropods).

    Therizinosaurs, especially more derived forms such as Nothronychus graffami, are thought to have been slow, large waddling, pot-bellied creatures rather than the quick, graceful gaited members of related Theropod predators. In spite of their likely herbivory, the group is thought to possess defensive capabilities with its powerful claws.

    The specimen of Nothronychus graffami (holotype UMNH VP 16420) was missing the skull, a majority of the cervical vertebral series and a few elements of the distal extremities (grayed-out bones). Missing elements of the skeleton were borrowed from Erlikosaurus andrewsi from Mongolia. The therizinosaur in the middle is a hypothetical feathered reconstruction and below, drawn with traditional scales.
    Modified from Zanno, 2009, Gillette, 2009 and Victor Leshyk and Plateau Magazine 2007.

    The tail was short and unnecessary for its mode of non-predatory diminished speed and thought to have provided upright, tripodal support for plant consumption. Unlike most theropods, the pes was curiously tetradactyl (four toes, which is a throwback to the ancestral dinosaur condition) with blunt unguals (claws), while its manus was tridactyl (three fingers) with elongated, recurved claws - the distinctive anatomical feature that gives the clade its name. Therizinosaur means "sickle-claw reptile". These Therizinosauroid features became increasing expressed from basal forms through more derived forms.

    Evolutionary osteological progression from basal Falcarius to Nothronychus.
    Take note of the increase in size, postural change, tail shortening, longer neck, size of the gut, massivity of the hindlimbs and acquisition of forelimb claws.
    Used with permission by Scott Hartman of

    What's more, being members of Theropoda, the entire clade was thought to possess rudimentary proto-feathers - integumentary-derived structures such as hair, scales and nails. Please visit my daughter's post on feathers here for the evolution of this dinosaurian structure.

    An imaginative interpretation of a proto-feathered adult therizinosaur accompanied by juveniles
    Used with permission by artist Damir G. Martin. Visit him here.

    Taking their singular, albeit bizarre morphology and fragmentary fossil record into account, it comes as no surprise that therizinosaurs have endured a convoluted taxonomic history within Dinosauria and have been variously assigned to nearly all of its major subclades.

    At one time, the family Therizinosauridae was referred to as the now-outmoded, group Segnosauria (segnis means slow in Latin) based on their heavy bodies, short legs, and sloth-like claws with a comparable lifestyle. They have been variously regarded as gigantic turtles, aberrant theropods and sauropodomorphs. Based on their retroverted (opisthopubic) pelvis (posteroventrally-directed pubis bone which was aimed backwards as in ornithischian, bird-hipped dinosaurs), they were considered to be phylogenetic intermediates between herbivorous prosauropods and early ornithischians.

    Pelvic girdle of a cast of Nothronychus graffami on display at the Carl Hayden Visitor Center at the Glen Canyon Dam. Although the therizinosaur is a Theropod, whose pubis is typically pointed forward, their pelvis is opisthopubic with the pubis bone retroverted, pointed backwards.

    With increasing numbers of discoveries in Asia and North America from the Cretaceous, the diversity of therizinosaurs has begun to exhibit remarkable growth. Yet, a significant impediment to ascertaining phylogenetic relationships has been the paucity of both ancestral and transitional forms. Speculation is gradually being replaced with resolution.

    Therizinosaurs are now considered to be unequivocal descendants not only of theropods but of the coelurosaurian clade and maniraptoran subclade with a sister relationship with Oviraptorosauria (see below). Thus, therizinosaurs are Saurischian, Theropodal, Tetanurian, Coelurosaurian, Maniraptoran dinosaurs and members of the family Therizinosauridea. 

    Therizinosaurs also share the tree with more highly derived Avialae (birds) and possess avian-associated characters such as a pneumatic-skeleton (hollow light-weight bones that facilitate a high rate of respiration, and later, powered flight), a pygostyle (shortened tail with fused vertebrae), feathers (for thermo-regulation, sexual dimorphism and brooding) and an avian-trending brain (for enhanced sight, sound and mechano-reception).

    One of many proposed Theropod phylogenies, the origin of facultative herbivory, that is omnivory, and the point of dietary diversification is posited at the base of Maniraptoriformes within the ellipse.
    Adapted from Zanno, 2009 and from Araujo et al, 2013.

    Interrelationships between specific therizinosaur taxa remains less clear. Until recently, the fossil record was restricted to Asia. With discoveries in North America such as Nothronychus mckinleyi (the first undisputed North American therizinosaurid from the Upper Cretaceous of New Mexico) and Falcarius utahensis (the third therizinosaur discovered in America, the most morphologically primitive therizinosaur yet discovered and a sister taxon to the clade of Therizinosauroidea from the Lower Cretaceous Cedar Mountain Formation of east-central Utah), we can begin to ask questions about origination, geographic and stratigraphic range, and even potential faunal mixing between immigrant and endemic clades. 

    One of many parsimonious phylogenies proposed for therizinosaurs
    50% Majority-rule consensus tree
    Modified from Pu et al, 2013.

    Did basalmost Falcarius utahensis originate in North America and certain populations expand into Asia? With recent finds in China such as Eshanosaurusdeguchiianus from the Early Jurassic, the presence of derived coelurosaurian lineages including therizinosaurians is being pushed back earlier. Did therizinosaurs differentiate from coelurosaurian ancestors before the breakup of Pangaea into Eurasia and North America and/or did they migrate across the tectonic Beringia Land Bridge that was established in the Early Cretaceous between northeast Asia and northwest North America? Was there more than one dispersal event? At various times, Asian endemic therizinosaurids show faunal similarities with North American forms. Did endemic forms mix with immigrant forms? Do North American therizinosaur taxa exhibit an Asian affinity or vice versa?   

    This imaginative diorama depicts a mix of Cretaceous fauna on the Beringia Land Bridge. A therizinosaur (in the box) has been tentatively identified on trackways in the Yukon.
    Illustration by Karen Carr and the Perot Museum of Science and Nature. Used with permission.

    Based on therizinosaur's osteological anatomy and soft tissue reconstructions, taking into account the habitats in which they likely thrived, and using animal analogues such as the sloth, certain dietary assumptions have been made about therizinosaurs and the Coelurosaurian clade in which they belong - once thought to have been obligate carnivores. In a little over a decade, doubt has been shed on that notion, raising the possibility or even likelihood that "dietary diversification was more commonplace among 'predatory' dinosaurs than previously appreciated" (Zanno, 2009).

    In fact, therizinosaurs are the most widely regarded candidate for herbivory among theropods. Dietary plasticity and facultative (capable of rather than restricted to) herbivory (omnivory) is thought to have afforded the group the potential to invade and exploit ecospaces early in evolution for survival.

    With a similar body shape and large claws on their front feet, Nothronychus graffami is shown as a bipedal browser analogous to the Giant Ground Sloth of the Ice Age.
    Artist Victor Leshyk

    Wayne Ranney and I met Merle bright and early at the Visitor Center in Big Water for a tour of the Moon. Crossing the dry streambed of Wahweap Creek, we travelled on a planar surface of Tropic mudstone, occasionally bouncing around on the hummocky, eroded terrain. The easiest places to build roads on the Colorado Plateau, although the most difficult places to maintain them, are on the Mancos-Tropic Shale. The soft rock weathers readily, forming broad, flat expanses and easy routes to get from here to there.

    Our first destination was the very spot of Merle's once-in-a-lifetime discovery. After a surprisingly short drive from the Visitor Center, we left our vehicle and began to ascend a large, loose mound of gray mudstone and claystone to a noticeably beveled off area. 

    Standing at the site of the former dig, let's let Merle tell the story. Although he's recounted the details many times in well over a decade since the find, it's clear that his enthusiasm hasn't diminished one iota. I'm filming, while Wayne is interjecting commentary. 

    The excavation consumed the better part of two years and included the removal of tons of overburden. Some of the skeletal elements were compressed by compaction, while the skeleton was slightly disarticulated due to settling after coming to rest in the soft marine sediments of the Tropic. The hillocks and empty washes in the Tropic Shale were created in more recent times as the flat-lying muddy sea bottom succumbed to the forces of erosion.

    Merle and Wayne debate the mysterious circumstances of the terrestrial therizinosaur's burial at sea.

    One important question that has plagued paleontologists is how the dinosaur came to be buried in marine mud 60 miles out to sea with the nearest shore confirmed geologically near present-day Cedar City? To date, no definitive answer exists, although theories include "bloat and float" - having died on or near land and washed out to sea buoyed by decomposing body-gases followed by burial- and "lost at sea" - a less plausible scenario of having been caught by a flood or storm, floated out to sea alive, perhaps attacked by predators, and eventually buried nearly fully articulated. The skeleton of N. graffami was located in a supine position, belly-up, implying that it settled to its final resting place in the Tropic mud while buoyed by gases in a typical death pose.

    I've seen the same "bloat and float" taphonymous (mode of fossilization) entity in New Jersey where terrestrial duck-billed dinosaur remains (the state fossil) have been found buried in glauconitic sands of the flooded Late Cretaceous continental shelf on Jersey farmland.

    As the Tropic continues to erode, a few small osseous remnants of N. graffami have weathered to the surface since its excavation over a decade ago. It's that fact, among many others, that keeps Merle coming back to The Moon. There's always something new to be found on the ever-changing landscape. Come back the next day, and a new discovery will be awaiting you. What appears to be a static landscape is entirely the opposite!


    Leaving the therizinosaur excavation site, we headed southeast on the flats of Wahweap Wash to further explore the Tropic's marine bounty.
    Is their any doubt that the Tropic is a marine deposit? This horizon is literally covered with disarticulated bivalves, typically inoceramids (clams), pycnodontids (oysters) and  a few ammonites. I've seen similar marine exposures in lag deposits of the Late Cretaceous marl of the New Jersey coastal plain but not as richly concentrated.
    Because of the fast rate of evolution in inoceramids and ammonites, they have become an important biostratigraphic tool for dating and identifying depositional boundaries in the Late Cretaceous of the Seaway - along with datable bentonite ash beds intermittently generated by volcanics to the west and southwest of the subsiding foreland. As a result, the Tropic Shale has been well constrained in the Kaiparowits Basin as upper Cenomanian-lower Turonian with Vasconceras diartianum-Prionocyclus hyatti ammonite biozones. 
    Turritella is an extremely common Cretaceous gastropod (snail) fossil in North America, whose descendants are still extant today. The shells are tightly-coiled and spiraled in the shape of elongated cones. In this region, the Tropic's mudstone-siltstone is highly-calcareous and extremely well-lithified. In the Kaiparowits Basin, the lower two-thirds is bluish-gray due to its high carbonate content; whereas, the upper third is darker and noncalcareous. Wayne suggested that it may have been diagenetically-altered.
    Notice that fine mudstone has entered and lithified within the Turritella's conical shell. When the shell eventually erodes away, it will leave a perfectly shaped internal cast called a steinkern (German meaning "stone" and "grain or kernal"). I found the identical gastropod in the Mancos Shale of the Seaway - the Tropic equivalent throughout the Southwest - near Ship Rock in northwestern New Mexico about 150 miles to the east.
    As sea level rose during the Seaways first transgression onto land, the Dakota Formation was deposited. With the sea's westward advance, deeper Tropic muds covered the Dakota, onlapping and interfingering with it. Walking the contact, we were able to view the bedding planes within the Tropic and the magnitude of layered invertebrate remains.
    The region is situated along the northern terminus of the Echo Cliff monocline, seen in the inclination of the landscape. Compressionally-generated monoclines formed across the Colorado Plateau with the ongoing subduction of the Farallon plate at a shallower angle during the Laramide orogeny.  
    We're walking on a Late Cretaceous marine and brackish-water oyster bed, where shells accumulated and became disarticulated, smashed by the high energy wave system nearshore. Some areas are depauperate, while others are so rich in bivalves that they formed a shell-pavement. 
    For every shark tooth I found, Merle's trained eye found ten - and in half the time. It was obvious that Merle possesses an uncanny ability of finding fossils. I asked him how he goes about looking it. He answered, "You need to have a second sense when you walk. I simply go where it feels right. That will lead you to bones and teeth."  There's a well-camouflaged Ptychodus tooth below concealed amongst mudstone rubble. 
    Of the many shark species that plied the Seaway, Ptychodus in the "Greenhorn Sea" was widespread. Ptychodus was a hybodontiform ("hump-backed" tooth) shark that lived from the Cretaceous to the Paleogene. It grew to 32 feet and was a benthic (bottom-loving) molluscivore (bivalve-loving) predator. The teeth are square or quadrilateral in shape, with broad, low crowns that overhang a blocky, short root. 
    Ptychodus teeth were arranged in straight, closely-spaced, parallel teeth rows that formed a bivalve-crushing pavement type of dentition.
    In addition to invertebrates, the Tropic Shale also contains an abundant and diverse marine vertebrate fauna including at least five different short-necked plesiosaur genera, two genera of turtles, a normal chondrichthyan-osteichthyan assemblage - and of course a therizinosaur dinosaur, albeit terrestrial. Owing to the poor preservation of the cartilaginous skeletal structures, chondrichthyans are represented largely by teeth and dermal ossicles. Here are some of the interesting remnants that we came across.
    This region of The Moon is on Bureau of Land Management land. The official website states  that visitors to BLM lands "are welcome to collect reasonable amounts of common invertebrate, such as ammonites and trilobites, and common plant fossils, such as leaf impressions and cones, without a BLM permit." Casual, hobby collecting is allowed "for non-commercial personal use, either by surface collection or the use of non-powered hand tools resulting in only negligible disturbance to the Earth's surface and other resources.”
    By noon, Merle, Wayne and I had spent considerable time baking in the sun with our heads trained downward, walking the Tropic and scouring the seabed for fossils. Notice the vehicle for scale. 
    A visit to the Tropic wouldn't be complete within mention of the indigenous vegetation. The Moon is sparsely vegetated, but Opuntia cacti add incredible color to the landscape, especially in Spring. Referred to as Prickly Pear, the brilliant crimson of this cactus is almost painful to the eyes in the bright sun. In the Southwest, there are many varieties all of which are native to the Americas. Many possess alkaloids with biological and pharmacological activities (for diabetes and hypertension). Most are edible, and some are used to make an alcoholic drink, while others have psychoactive properties.
    This hardy shrub of Prince's Plume, in the mustard family, is highly recognizable by the bright yellow flowers clustered along the stem. It's native to the western United States and prefers alkaline and gypsum-rich soils, typically found in deserts. The plant is toxic since they concentrate selenium from the soil, necessary for cellular function. Coincidentally, selene means "moon" in Greek.

    Desert Globemallow is also native to the American Southwest and grows well in alkaline, sandy soil and clay. The plant was used by Native Americans as a food source and for medicinal purposes. 
    Back at the Visitor Center in Big Water, Wayne and I got the grand tour of the facility. Merle is an extremely personable and friendly guy, who is very affable and chock full of stories. In all, it was a fantastic and memorable day walking The Moon of Big Water with Merle's paleontological prowess and Wayne's geological knowledge.   
    • A New North American Therizonosaurid and the Role of Herbivory in Predatory Dinosaur Evolutionby Lindsay E. Zanno  et al, Proceedings of the Royal Society, 2009.
    • Ancient Landscapes of the Colorado Plateau by Ron Blakey and Wayne Ranney, 2008.
    An Unusual Basal Therizinosaur Dinosaur with an Ornithischian Dental Arrangement from Northeastern China by Pu et al, 2013. 
    • A Taxonomic and Phylogenetic Re-evaluation of Therizinosauria (Dinosauria:
    Maniraptora) by Lindsay Zanno, Journal of Systematic Paleontology, 2010.
    • At the top of the Grand Staircaseby Alan L. Titus and Mark A. Leowen, 2013.
    Correlation of Basinal Carbonate Cycles to Nearshore Parasequences in the Late Cretaceous Greenhorn Seaway by William P. Elder et al, 1994.
    Discovery and Excavation of a Therizinosaurid Dinosaur from the Upper Cretaceous Tropic Shale (Early Turonian), Kane County, Utah by David D. Gillette et al, 2002.
    • First Definitive Therizinosaurid From North America by James I. Kirkland and Douglas G. Wolfe, 2001.
    • Fossils from the Tropic Shale by Merle H. Grafam, 2000. Personal copy from the author.
    • Geological Evolution of the Colorado Plateau of Eastern Utah and Western Colorado by Robert Fillmore, 2011.
    • Geology of the American Southwest by W. Scott Baldridge, 2004.
    • Geology of Utah's Parks and Monuments, Utah Geological Association by Douglas A. Sprinkel et al, 2003.
    Herbivorous Ecomorphology and Specialization Patterns in Theropod Dinosaur Evolution by Lindsay E. Zanno and Peter J. Makovicky, 2011.
    On the Earliest Record of Cretaceous Tyrannosaurids in Western North America: Implications for an Early Cretaceous Laurasian Interchange Event by Lindsay E. Zanno and Peter J. Makovicky, 2010.
    • The Geology of the Grand Staircase in Southern Utah by the Geological Society of America, 2002.
    • The Pectoral Girdle and Forelimb of the Primitive Therizinosaiuriod Falcarius Utahensis by Lindsay A. Zanno, 2006.
    • Therizinosaur -  Mystery of the Sickle-Claw Dinosaur by David D. Gillette, Arizona Geology, Published by the Arizona Geological Survey, 2007.
    • Therizinosaur – Mystery of the Sickle-Claw Dinosaur by David D. Gillette, Ph.D., Plateau, Museum of Northern Arizona, 2007.
    • Vertebrate Paleontology by Michael J. Benton, 2005.

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    In “101 American Geo-Sites You’ve Gotta See,” author Albert B. Dickas listed Maryland's Calvert Cliffs as number 32. With curiosity piqued and the Cliffs renowned for their diverse and well-preserved fossiliferous assemblages - having attracted tourists and scientists as early as 1770 - I decided to visit the site in July. Only a 90 minute drive southeast of Washington, the Calvert Cliffs is a spectacular and scenic, almost continuous 50 km wavecut bluff along the western side of the Chesapeake Bay.

    A geological contradiction to the Eastern Seaboard's otherwise flat Coastal Plain, the Cliffs rise in places to as much as 40 meters. They are cut into actively eroding, unconsolidated sandy, silty and clayey sediments of the lowermost portion of the Chesapeake Group. Throughout much of the Miocene, the region was the site of a shallow, inland arm of the temperate Atlantic Ocean during climatic cooling, uplift of the Atlantic Coastal Plain and eustatic changes in sea level. The stratal package preserves the best available record of middle Miocene marine and, less frequently, terrestrial life along the East Coast of North America.


    Looking obliquely at Calvert Cliffs from the cuspate foreland at Flag Ponds, the undeformed beds of the Chesapeake Group can be seen to have a regional dip of less than one degree to the southeast (about 2m/km). That allows the exploration of progressively younger strata in a southward direction and vice versa. The strata is primarily Miocene with a coarse-channel, fluvial and tidal deposited overburden variably from the Pliocene and Pleistocene. Typical of bluffs adjacent to the bay, the beach and cliff-vegetation is small or non-existent. Notice the slump and collapse material at the base. Its presence at the toe is generally short-lived. The beach at Flag Ponds is very popular for sunning, swimming and strolling, but fossil collecting at the cliff-toes, which is a very productive locale, is prohibited and prevented by the presence of a large fence.

    The recorded history of the Chesapeake region is as varied as the geology, which began with the Spanish. The cartographer Diego Gutierrez recorded the Chesapeake on a map, calling it “Bahia de Santa Maria.” The English arrived with John White in 1585 and again in 1608 with John Smith’s entry onto the Calvert Peninsula. His mission was to explore the Chesapeake region, find riches, and locate a navigable route to the Pacific, all the while making maps and claiming land for England. On John Smith’s 1606 map (below), the Calvert Cliffs were originally called “Rickard’s Cliffes”, after his mother’s family name. 

    The first English settlement in Southern Maryland dates to somewhere between 1637 and 1642, although the county was actually organized in 1654. Established by Cecelius Calvert, the second Lord Baltimore, English gentry were the first settlers, followed by Puritans, Huguenots, Quakers, and Scots. In 1695, Calvert County was partitioned into St. Mary's, Charles, and Prince George's, and its boundaries became substantially what they are today. Statehood wasn’t granted to Maryland until 1788. The Revolutionary War, the War of 1812 and the Civil War waged in the region. In fact, the peninsula was the training site for Navy and Marine detachments, and the invasion of Normandy was simulated on the lower Cliffs of Calvert.

    John Smith's 1606 map of the Chesapeack (correct spelling) Bay. Note the location of Rickards Cliffes (English spelling) emptying into the Virginia Sea (aka Atlantic Ocean). North is to the right. Maryland was granted statehood in 1788 with the region referred to as Virginia.

    The Cliffs of Calvert reside on the broad, flat, seaward-sloping landform of the Coastal Plain of Maryland on the western shore of the Chesapeake Bay in Calvert and southernmost Anne Arundel Counties. Located on finger-like Calvert Peninsula, the Cliffs are on the higher western section of the Plain, while the lower section, known as the Eastern Shore (always capitalized), is a flat-lying tidal stream-dissected plain, generally less than 60 feet above sea level. 

    Red arrow indicates the region of Calvert Cliffs on the Atlantic Coastal Plain of the eastern shore of the Calvert Peninsula within the Chesapeake Bay.
    Modified from USGS map

    Chesapeake Bay is an estuary - the largest of 130 in the United States - with a mix of freshwater from the Appalachians and brackish water from its tidal connection to the Atlantic Ocean. The Bay's central axis formed by the drowning of the ancestral Susquehanna River by the sea that flowed to the Atlantic from the north during the last glacial maximum of the Pleistocene Ice Age some 20,000 years ago - when the planet's water was bound up in ice and global seas were lower.

    Multiple advances of the Laurentide Ice Sheet blanketed Canada and a large portion of northern United States during Quaternary glacial epochs. Its advance never reached the region of Chesapeake Bay, having extended to about 38 degrees latitude. Being in a contemporary interglacial period - the Holocene - global seas are higher, but not at the level during the deposition of the Chesapeake Group at Calvert Cliffs during the Miocene.  

    During the time of deposition of the Calvert Cliffs, fluctuating seas drowned portions of southern Maryland. A shallow, protected basin of the Atlantic Ocean called the Salisbury Embayment was located in Virginia, Maryland, Delaware and southern New Jersey. It was one of many depocenters along the Eastern Seaboard, separated by adjoining highs or arches. The Salisbury Embayment structurally represents a westward extension of the Baltimore Canyon Trough that extends into the central Atlantic on the continent's shelf and slope.

    Major Structural Features of the Atlantic Coastal Plain from New York to Florida
    The embayments are depocenters - major sites of sediment accumulation. The Fall Line is the inner limit of deposits on the Coastal Plain at the Appalachian Piedmont Province. The Salisbury Embayment extends westward to the Fall Line.
    Modified from Ward and Strickland, 1985.

    The depositional history and relief of the Cliffs of Calvert are testimony to the elevated level of the seas in the Miocene. In addition, the Embayment resides on the “passive” margin of North America’s east coast, which is typified by subsidence and sedimentation rather than seismic faulting and volcanic activity found on the continent’s “active” west margin. The Embayment was and is in a constant dynamic state - passive but far from inactive. 

    How did the passive margin and the Coastal Plain of Maryland form geologically? What is the sediment source of the depocenters? What fauna occupied the ecosystem of Calvert Cliffs? These questions can't be adequately addressed without gaining an appreciation for the geological evolution of North America's East Coast. Here's a brief synopsis.

    The supercontinent of Rodinia fully assembled with the termination of the Grenville orogeny in the Late Proterozoic and brought the world's landmasses into unification. Rodinia's tectonic disassembly in the latest Proterozoic gave birth to the Panthalassic, Iapetus and Rheic Oceans, amongst others. Rodinia's fragmentation was followed by the supercontinent of Pangaea's reassembly from previously drifted continental fragments throughout the Paleozoic. 

    A succession of orogenic events...
    Using modern co-ordinates, the east coast of Laurentia (the ancestral, cratonic core of North America) experienced a succession of three major tectonic collisions during Pangaea's assembly – the Taconic (Ordovician-Silurian), Acadian (Devonian-Mississippian) and Alleghanian (Mississippian-Permian) orogenies. Each orogen built a chain of mountains that overprinted those of the previous event - closed intervening seas and added crust to the growing mass of the continent of North America. 

    The Paleozoic Assembly of Pangaea
    In the Early Devonian (400 Ma), following the Taconic orgeny, the Acadian collisional event has initiated mountain building on Laurentia's east coast with the closure of the Iapetus Ocean. The megacontinent of Gondwana, lying across the Rheic Ocean, is converging upon Laurentia towards its eventual subduction zone.
    Modified from Ron Blakey and Colorado Plateau Geosystems. Inc.

    A final orogeny assembles Pangaea...
    The penultimate Alleghanian orogeny between Laurussia (Laurentia, Baltica and Eurasia) and the northwest Africa portion of Gondwana - the two largest megacontinental siblings of Rodinia's break-up - culminated with the late Paleozoic formation of Pangaea. That unification event constructed the Central Pangaean Mountains - a Himalayan-scale, elongate orogenic belt some 6,000 km in length within Pangaea at the site of continental convergence. Calvert Cliffs (red dot) had not yet evolved, but its deep Grenville basement was in place along with the orogen that would eventually blanket its coastal seascape with sediments from the highlands.

    The Supercontinent of Pangaea
    By the Late Pennsylvanian (300 Ma), the closure of the Rheic Ocean brought various microcontinents, magmatic arcs, and the northwest African and Amazonian aspect of Gondwana into an oblique transpressive collision with Laurussia (summarily Laurentia, Scandinavia and Eurasia). Convergence built the elongate Central Pangaean range composed of segments from South America and Mexico through North America and into Europe and Asia. The Chesapeake Bay, yet to form, is landlocked at the red dot.
    Modified from Ron Blakey and Colorado Plateau Geosystems. Inc.

    Supercontinental fragmentation...
    Beginning in the Late Triassic, Pangaea’s break-up created a new ocean – the Atlantic – and fragmented the Pangaean range. As a result, the Appalachian chain remained along the passive eastern seaboard of the newly formed continent of North America from Newfoundland to Alabama, while severed portions of the range were sent adrift on rifted continental siblings. A supercontinental tectonic cycle is apparent between Grenville formation of Rodinia and its fragmentation and Alleghanian formation of Pangaea and its dissassembly.

    The orogen's remnants form the Anti-Atlas Mountains in western Africa, the Caledonides in Greenland and northern Europe, the Variscan-Hercynian system in central Europe and central Asia, the Ouachita-Marathons in south-central North America, the Cordillera Oriental in Mexico, and the Venezuelan Andes in northwestern South America. As a result of Pangaea's fragmentation, the region of the future Calvert Cliffs (red dot) was finally positioned in proximity to the sea, awaiting the orogen to erode and Cenozoic eustasy to flood the landscape and deposit the Chesapeake Group during the Miocene.

    The Continent of North America
    The Atlantic Ocean began to form with the disassembly of Pangaea in the Late Triassic. In the Late Jurassic (150 Ma), the modern continents are drifting apart. The Appalachian Mountain range has begun to erode and shed its deposits on the developing Atlantic Coastal Plain (light blue). The Chesapeake Bay, yet to form, is located at the red dot.
    Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

    North America's new passive margin...
    By the Cretaceous, the Appalachian highlands had eroded to a nearly flat peneplain, sending voluminous fluvial sediments to the continental margin and shelf in a seaward-thickening wedge. Under the weight and the effect of lithospheric cooling, the passive marginal shelf began to subside and angle seaward as global warming and rising seas drowned both the coast and cratonic core of North America. The Salisbury Embayment, along with others up and down the coast in a scalloped array, was created by the tilting and reactivation of normal faults that extended westward to the Appalachian foothills. Initially, the regional dip was to the northeast, but Neogene uplift left the Coastal Plain's beds dipping to the southeast.

    North America in the Late Cretaceous (89 Ma)
    The entire shallow, subsiding passive margin of North America's east coast (light blue), along with the depocenters of the Salisbury Embayment (ellipse), were drowned by global high seas beginning in the Late Cretaceous. Notice that the cratonic core of Laurentia has been submerged by two converging arms of the sea from the north and south that formed the Western Interior Seaway. Also, notice the narrow active margin at North America's west coast, the site of convergent tectonics. This eustatic condition will not prevail with sea level progressively dropping as it fluctuated throughout the Pliocene, the Pleistocene and Holocene.
    Modified from Ron Blakey and Colorado Plateau Geosystems. Inc.

    Subsidence and sedimentation...
    Although classified as a passive continental margin, the "active" shelf received nonmarine 
    deposition through most of the Cretaceous. With the exception of the Oligocene, the Tertiary saw wave after wave of marine deposition on Maryland's subsiding shore spurned by rising global seas. During the Late Oligocene, Miocene and early Pliocene, the Chesapeake Group was deposited. The Group's lower three stratal components are exposed as wave-eroded bluffs at Calvert Cliffs. Their ~70 m of strata preserve nearly 10 million years of elapsed time. It forms the most available sequence of exposed Miocene marine sediments along the East Coast of North America.

    The depocenter of the Salisbury Embayment is drowned by high seas during the Middle Miocene (15 Ma). This eustatic condition will not prevail with sea level progressively dropping as it fluctuated throughout the Pliocene, into the Pleistocene and present.
    Modified from Ron Blakey and Colorado Plateau Geosystems. Inc.

    The Chesapeake Group's Cliffs of Calvert...
    Vacillating seas consequent to Pleistocene glaciation-deglaciation periodically flooded and exposed the land, backflooding rivers and bays such as the Chesapeake. Our present interglacial epoch - the Holocene - has re-exposed the Chesapeake Group and the Cliffs of Calvert to erosion. In spite of not having experienced a significant phase of tectonic convergence for over 200 million years, the modern Appalachian Mountains have been rejuvenated during the late Cenozoic, possibly isostatically in response to ongoing erosion or by mantle forcing. That contributed to river incision and deposition across the Coastal Plain with sedimentation such as the Chesapeake Group.

    A glowing Maryland sunrise illuminates the strata of the Calvert Cliffs looking south.
    Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum

    North America's most easterly geomorphologic region is the siliciclastic sedimentary wedge of the Atlantic Coastal Plain that began to form with the breakup of Pangaea. It’s a low relief, gentle sloped, seaward-dipping mass of unconsolidated sediment over 15,000 feet thick, deposited on the margin of North America Appalachian-derived rivers and streams, and spread back and forth by the migrating shorelines of vacillating seas throughout the Cenozoic. In Maryland, progressing to the northwest from the Coastal Plain, one encounters the Piedmont Plateau at the Fall Line, the Blue Ridge, the Valley and Ridge and the Appalachian Plateau Provinces.

    From east to west through the Appalachian orogen with an underlying Grenville basement, the physiographic provinces of Maryland are synonymous with those up and down the East Coast of North America. Notice the Fall Line, separating the Piedmont from the Coastal Plain, and the Chesapeake Bay, dividing the Plain into higher western and lower eastern subdivisions.

    The five physiographic provinces are a series of belts with a characteristic topography, geomorphology and specific subsurface structural element. The overall trend is from  southwest to northeast along the eastern margin of North America. Their strike and geologic character have everything to do with the tectonic collisions that built mountains, recorded periods of quiescence, formed and fragmented at least two supercontinents, and opened and closed the oceans caught in between.

    Location of Calvert Cliffs on the Chesapeake Bay's western shore of the Atlantic Coastal Plain (light colored)
    Modified from USGS map

    Calvert Cliffs is on the Chesapeake Bay's western shore of the Atlantic Coastal Plain, as are the major cities on the mid-east coast - Philadelphia, Baltimore, Richmond, Washington, etc. If you connect them on a map, you'll locate the approximate western boundary of the Coastal Plain called the Fall Line or Zone. It's the geomorphic break (and geographic obstacle) where a 900-mile long escarpment of falls and rapids separates the Coastal Plain from hard, metamorphosed crystalline rock of the Piedmont foothills to the west.

    The Piedmont and Blue Ridge share similar types of crystalline igneous and metamorphic rocks of the core of the Appalachians. The majority of Blue Ridge rocks are related to events of the Precambrian and Cambrian from Grenville mountain building to the Cambrian rift basins, while most of the Piedmont rocks were transported and accreted to North America. A discussion of the details of tectonic derivation and geologic structure of the remaining westerly provinces is beyond the scope of this post. 

    The Calvert Cliffs consist largely of relatively undeformed and unlithified strata of silts, sands and clays of the Calvert, Choptank and St. Mary's formations (Shattuck, 1904) in ascending order of the Chesapeake Group. The formations are interrupted by a series of erosional unconformities and other hiatal intervals and preserve nearly 10 million years of elapsed time.

    Flag Ponds Nature Park
    The cliffs in the distance are the same as the top of the post. Bluffs directly adjacent to the bay generally have very narrow or no beach material (0-3 m) and little to no vegetation on the face. The erosion rate there is historically uniform (0.3-0.6 meters per year), where they are susceptible to slumping and collapse facilitated by a slope angle of nearly 70 degrees. In this area of Calvert Cliffs and Cove Point to the south, "fossil" bluffs are stabilized and preserved inland of the shoreline as the beach acts as a barrier and protects toe slope erosion from wave action as it migrates to the south along longshore currents. At Cove Point the migrating-landform is a prograding cuspate foreland. Southward bluffs become protected from wave action as new beaches are deposited at the bluff-toes. As the foreland migrates to the south, the beach will recede and active bluff erosion will recommence. The changes induced by the foreland occur on a "decadal rather than centennial scale, which places the rate of slope failure on a human scale." This passive Atlantic margin is anything but!
     (Martha Herzog, USGS).

    The Miocene succession was deposited as a complex package representing a first-order transgressive-regressive cycle with numerous superimposed smaller-scale perturbations of sea level. Overall, the record is one of gradual shallowing within the Salisbury Embayment and is reflected in the character of the strata that progresses from inner to middle shelf to tidally-influenced, lower-salinity coastal embayments. Deposition occurred under subtropical and warm temperate conditions in a shallow marine shelf environment at a maximum water depth of more than ~40-50 meters.

    The exposures include not only the Calvert Cliffs but the Westmoreland and Nomini Cliffs along the Virginia Shore of the Potomac River. Debated for more than a century, estimates for the basal Calvert range from early Early Miocene to mid-Middle Miocene. 

    Miocene Stratigraphy of Calvert Cliffs
    The lower Chesapeake Group's Miocene section has been subdivided using a multitude of stratigraphic systems including three formations of 24 stratigraphic beds and molluscan zones, many of which have been renamed as members based on locality. In addition, various depositional sequences and events have been described.  Dates are in millions of years (Ma).
    Modified from Ward and Andrews, 2008, and Carnevale et al, 2011.

    A general absence of beaches below the cliffs is a characteristic of the region. Direct wave undercutting at the cliff-toe, freeze-thaw erosion, underground seepage at sand-clay interfaces and mass-wasting (the average inclination is 70 degrees) are accompanied by rapid wave removal of colluvium (slope debris). Long-term rates can exceed 1 m/yr. Slumps, rotational slides and fallen trees are constantly being generated and removed. For these reasons, beachcombing for fossils and excavating the cliff-toes is a dangerous and prohibited venture. Collected is allowed in designated parks along the shoreline such as Calvert Cliffs State Park, Flag Ponds Nature Park and Brownies Beach, and private beaches given the owner's permission. 

    Two vying factions in regards to the Cliffs are scientists that reap the benefit of ongoing erosion and the homeowners, who seek real estate in close proximity to the cliff edge for the sake of a bay view. For the former, the best way to preserve the Cliffs is to let them erode naturally, while the latter would like to riprap (with stone or concrete), bulkhead, sandbag and groin-field the Cliffs to preserve them and their property. In dealing with Mother Nature, in this regard, shoreline protection reduces the risk of cliff failure, although it doesn't eliminate it. It's only a matter of geologic time. 

    Rocky Point just downbay (south) of the Calvert Cliffs Nuclear Power Plant
    Exposed are the Choptank and the St. Mary's Formations, the latter often oxidized to an orange color. The boundaries between the members and subdivisions are readily discernible. Zonation of thinly laminated beds of cobbles, mollusk shells, molds and casts can be made out even at this distance. Uppermost strata (upland deposits) consists of undulating Pleistocene alluvium, possibly where Pliocene beds were beveled off during a Pleistocene embayment. Again, notice the slump and collapse material, and destabilized trees sliding down the slope from above. Many homes perched on the cliff-edge have met a similar fate.
    Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum

    To reach otherwise inaccessible sections of the Cliffs and lessen the inherent dangers of collapse and burial, this mode of exploration employs descent from above. Excavation into the unlithified substrate is facilitated by an air-powered drill using a scuba tank's compressed air.

    From Google Science Fair 2014. See the video here.

    The formations preserve more than 600 largely marine species that include diatoms, dinoflagellates, foraminiferans, sponges, corals, polychaete worms, mollusks, ostracods, decapods, crustaceans, barnacles, brachiopods and echinoderms. The macrobenthic fauna (large organisms living on or in the sea bottom) act as good indicators of salinity. The Calvert and Choptank are dominated by diverse assemblages of stenohaline organisms (tolerating a narrow range of salinity); whereas, the younger St. Mary's Formation exhibits an increasing prevalence of euryhaline molluscan assemblages (tolerating a wide range of salinity). The changes within the assemblages reflect the fluctuating freshwater conditions within the Salisbury Embayment.  

    Vertebrate taxa include sharks and rays, actinopterygian fish, turtles, crocodiles, pelagic (open sea) birds, seals, sea cows, odontocetes and mysticetes (whales, porpoises and dolphins).

    In addition, the Cliffs preserve isolated and fragmentary remains of large terrestrial mammals (peccaries, rhinos, antelope, camels, horses and an extinct group of elephants called gomphotheres), palynomorphs (pollens and spores), and even land plants (from cypress and pine to oak) that bordered the Miocene Atlantic Coast and were carried to the sea by floodplains, rivers and streams sourced by the Appalachians.

    In the Miocene, mammalian diversity was reaching unprecedented levels, increasing in size and filling every conceivable niche on every continent. Grass-grazing, multi-stomached herbivorous artiodactyls (such as giraffes, antelopes, cattle, camel, pigs and hippopotami) were slowly replacing dominant perissodactyls (such as horses, rhinos and tapers) that developed after the end-Cretaceous extinction.  
    Modified from Jay Matternes

    Miocene River Environment by Karen Carr with permission

    Armed with a plastic garden rake in hand from the local hardware store, I collected this fossil potpourri (below) on a brief 60 minute stroll along the beach at Flag Ponds. Their abundance and availability is a testimony to the richness and diversity of the Miocene marine fauna. The fossils are continually being generated from the eroding cliffs and their underwater extensions. 

    I am uncertain as to the specific origin of the mammalian bony fragments, but I suspect they are largely from marine fauna (i.e. dolphin, whale, seal, etc.) rather than terrestrial, since the former vastly outnumber the latter. Cetaceans such as the whale have repurposed an air-adapted mammalian ear for the differentiation of underwater sounds. The shell-like otic tympanic bulla is a thickened portion of the temporal bone located below the middle ear complex of bones. The large dense bone is well preserved and can easily be mistaken for an eroded fragment of rock.

    The crocodile tooth is an indication that rivers and swampy habitats existed in the marginal marine environment of Calvert Cliffs. Shark teeth are the most common vertebrate fossils preserved at the Cliffs. Their numbers are commentary on the favorable paleoenvironmental conditions that existed in the Salisbury Embayment. Of course, sharks continually produce and shed teeth throughout their lives, facilitated by the absence of a long, retentive root structure, and are composed of durable and insoluble biogenic apatite, which favors their preservation. Calvert Museum collections contain as many as 15 genera. The main constituents are Carcharhinus, Hemipristis, Galeocerdo, Isurus and Carchrius. Carcharhiniformes shed about 35,000 teeth in a lifetime!

    Appearing in the fossil record about 395 million years ago (middle Devonian), the Class Chondrichthyes (cartilaginous skeletal fish) is divided into two subclasses: Elasmobranchii, which includes sharks, rays and skates, and Holocephali (chimaeras). Elasmobranchii are distinguished by their 5-7 pairs of gill clefts, rigid dorsal fin, presence or absence of an anal fin, placoid dermal scales, teeth arranged in series within the jaws and the upper jaw being not fused to the cranium. Along with a dolphin tooth and a few gastropods, here are a few specimens collected from the surf at Calvert Cliffs State Park, about five miles southeast of Flag Ponds. 

    Top Row: Hemipristis (Snaggletooth shark), Isurus (?), Carcharhinus (?)
    Middle Row: Carcharhinus (?), Hemipristis (?), Porpoise tooth, Hemispristis (?)
    Bottom Row: Ray plate, Turritella shell, ray plate, Scaphopoda mollusc shell.
    Any corrections or additional insight regarding these fossils is welcomed.

    From these small samples, one can glean the ancient habitat at Calvert Cliffs during the Miocene. The combined study of both fossils and rock layers are essential in reconstructing the paleo-geography of the Cliffs. 

    By far, the largest but rarest shark teeth at Calvert Cliffs (but widely distributed within the world's oceans) are those of a "Megalodon," an extinct species of shark that lived from the late Oligocene to early Pleistocene (~28 to 1.5 million years ago). Its distinctive triangular, strongly serrated teeth are morphologically similar to those of a Great White shark (Carcharodon carcharias), a fact that fuels the debate over convergent dental evolution versus an ancestral relationship.

    An allometric relationship exists between tooth width and body length in modern sharks. A tooth that is 5.5 inches wide correlates with a body length of 60 feet, making Megalodon the largest shark to have lived, weighing as much as 100 tons. I calculated this Megalodon tooth in my collection to come from a 49 footer. That's ten feet longer than a school bus!

    The controversy has resulted in a taxonomic name of either Carcharodon megalodon or Carcharocles megalodon - commonly abbreviated as C. megalodon. The “Meg” is regarded as one of the most powerful apex predators in vertebrate history. On rare occasion, extinct cetacean fossilized vertebrae have been uncovered with bite-marks suggestive of mega-tooth shark predation or scavenging. Megalodon is represented in the fossil record by teeth and vertebral centra, since the majority of its cartilaginous skeleton is poorly preserved.

    C. megalodon dining on cetaceans
    With permission from artist Karen Carr with permission

    Dr. Stephen Godfrey of the Calvert Marine Museum has been conducting paleontological studies in the Calvert Cliffs for some 15 years. After rafting along the shoreline to the excavation site, this paleontologist is taking measurements of a trace fossil interpreted as an infilled tilefish burrow from the Plum Point Member of the Calvert Formation deposited some 16 million years ago. In a 2014 paper in the JVP (see reference below), well preserved,  partially complete, largely cranial remains of tilefish are described. They have been collected over the past three decades from Miocene deposits outcropping in Maryland and Virginia. 

    Ruler in hand, paleontologist W. Johns investigates the exposed tilefish burrow.
    Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum

    Lopholatilus ereborensis, a new species of family Malacanthidae and teleost (infraclass of advanced ray-finned fish), inhabited long funnel-shaped vertical burrows that it excavated for refuge within the cohesive bottoms of the outer continental shelf of the Salisbury Embayment that likely inhabited other parts of the warm, oxygenated waters of the western North Atlantic outer shelf and slope. The species name was derived from 'Erebor,' the fictional name for the Lonely Mountain in J.R.R. Tolkien's The Hobbit. Like the mountain-clan of dwarves, the tilefish mined the substrate.

    This is a close-up view of an infilled, cylindrical-shaped, tilefish-excavated burrow in erosional cross-section. Investigations of extant tilefish show they were shelter-seeking within horizontal clay substrates. The tilefish used as a head-first entrance and tail-last exit for protection from predators. The burrows were subject to infill and collapse, taphonomously preserving the tilefish if within.
    Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum

    Schematic drawing showing three Miocene tilefish burrows. The fish on the left is actively excavating a new burrow. In the center, the burrow has been infilled, preserving the fish that habitated the burrow. On the right, the fish has taken refuge within its burrow.
    Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum

    Lopholatilus ereboronsis moderately deep skull and short snout in left lateral view with interpretive illustration. For orientation, the large circular structure is the orbit with anterior to the left. Post-cranial structures (vertebral skeleton) are missing. The fossil preserves anatomical detail as if a live dissection. One can clearly differentiate the entire suspensorium (jaw connections) of the maxilla (upper jaw) and a few teeth, the dentary (lower jaw) and the quadrate (ancestral jaw-joint), etc. Five extant genera of tilefish inhabit the waters of the Atlantic, Indian and Pacific Oceans.
    Photo Courtesy of Stephen J. Godfrey, Ph.D., Curator of Paleontology, Calvert Marine Museum

    In an attempt to see what fossilized remains might have filtered down from overlying Miocene and more recent strata, I walked the beach until finding a break where a wash had carved a trough through the bluffs. I immediately spotted a white object glistening in the sun in a stream bed filled with gravel and tiny sharks teeth that turned out to be the worn remnants of a Colonial-era smoking pipe.

    Pipes of clay were first smoked in England after the introduction of tobacco from Virginia in the late 16th century. Sir Walter Raleigh, an English sea captain, was one of the first to promote this novel habit acquired from Native Americans that practiced its ritual use for many centuries. By the mid-17th century clay pipe manufacture was well established with millions produced in England, mainland Europe, and the colonies of Maryland and Virginia. For various reasons, clay pipe demand declined by the 1930’s.

    Clay pipes were very fragile and broke easily, and along with their popularity, they are commonly found at Maryland and Virginia colonial home sites. In Colonial-era taverns, clay pipes that were passed around were supposedly broken off at the stem for the next user in the interest of hygiene. Some clay pipes can be dated by the manufacturer's stamp located on the bowl, which was unfortunately missing in this lucky (but well calculated) find.

    • Evolution of Equilibrium Slopes at Calvert Cliffs, Maryland by Inga Clark et at, Shore and Beach, 2014.
     •Frequency of Effective Wave Activity and the Recession of Coastal Bluffs: Calvert Cliffs, Maryland by Peter R. Wilcock et al, Journal of Coastal Research, 1998.
    • Geologic Evolution of the Eastern United States by Art Schultz and Ellen Compton-Gooding, Virginia Museum of Natural History, 1991.
    • Maryland's Cliffs of Calvert: A Fossiliferous Record of Mid-Miocene Inner Shelf and Coastal Environments by Peter R. Vogt and Ralph Eshelman, G.S.A. Field Guide, Northeastern Section, 1987.
    • Miocene Cetaceans of the Chesapeake Group by Michael D. Gottfried, Proceedings of the San Diego Society of Natural History, 1994.
    • Miocene Rejuvenation of Topographic Relief in the Southern Appalachians by Sean F. Gallen et al, GSA Today, February 2013.
    • Molluscan Biostratigraphy of the Miocene, Middle Atlantic Coastal Plain of North America by Lauck W. Ward, Virginia Museum of Natural History, 1992.
    • Slope Evolution at Calvert Cliffs, Maryland by Martha Herzog, USGS.
    • Stargazer (Teleostei, Uranoscopidae) Cranial Remains from the Miocene Calvert Cliffs, Maryland, U.S.A. by Giorgio Carnevale, Stephen J. Godfrey and Theodore W. Pietsch, Journal of Vertebrate Paleontology, November 2011.
    • Stratigraphy of the Calvert, Choptank, and St. Mary's Formations (Miocene) in the Chesapeake Bay Area, Maryland and Virginia by Lauck W. Ward and George W. Andrews, Virginia Museum of Natural History, Memoir Number 9, 2008.
    • The Ecphora Newsletter, September 2009.
    • Tilefish (Teleostei, Malacanthidae) Remains from the Miocene Calvert Formation, Maryland and Virginia: Taxonomical and Paleoecological Remarks by Giorgio Carnevale and Stephen J. Godfrey, Journal of Vertebrate Paleontology, September 2014.
    Variation in Composition and Abundance of Miocene Shark Teeth from Calvert Cliffs, Maryland by Christy C. Visaggi and Stephen J. Godfrey, Journal of Vertebrate Paleontology, January 2010. 

    I wish to express my gratitude and thanks to Stephen J. Godfrey, PhD., Curator of Paleontology of the Calvert Marine Museum, for providing valuable support (personal communications, October 2014), documentation and photographs of Calvert Cliffs and his recent excavation and publication.

    Calvert Cliffs Marine Museum was founded in 1970 at the mouth of the Patuxent River in Solomons, Maryland. Visit them here, but do go there! You can join the museum here.

    The Ecphora is the quarterly newsletter of the Calvert Marine Museum Fossil Club. Ecphora gardnerae gardnerae is an extinct, Oligocene to Pliocene, predatory gastropod and the Maryland State Fossil, whose first description appeared in paleontological writings as early as 1770. Sadly, riprapping (rock used to protect shorelines from erosion) has covered one of only two localities in the State of Maryland where the fossil can be found. The other is on private land and off limits without permission. Ironically, Marylanders can find their state fossil in Miocene strata of Virginia. Download copies of current and past newsletters here or simply subscribe.

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    “There are trees, and then there are trees.”
    Dick Byrd, 2014

    My neighbor, Dick Byrd of Newton, Massachusetts, has a lot to be thankful for. One of his biggest joys is growing or should I say towering in his front yard. It’s a tree, but not just any tree. It’s an Eastern Hophornbeam, and it’s the National Champion – the largest of its species growing in the United States!

    We all know that a champion is a person who has defeated or surpassed all of his/her rivals in a competition. It includes someone who fights or argues in support of another person, cause or belief. But what's a champion tree?

    It will come as no surprise, that to qualify, a tree must be big. It must be the largest species according to a standard measuring formula, and it must be re-measured every 10 years in order to maintain its champion status. To be eligible, a tree must be native to or naturalized in the continental United States, including Alaska but not Hawaii.

    American Forests is the oldest national nonprofit conservation organization in the United States. Their mission is to restore threatened forest ecosystems and inspire people to value and protect urban and wildland forests. Since 1940, their National Big Tree Program has been a testament to American Forests’ legacy of leadership in recognizing the beauty and critical ecosystem services provided by the country's biggest and oldest trees. More than 750 champions are crowned and documented in their biannual American Forests Champion Trees national register, located here.

    For more than 70 years, the goal of the program has remained to preserve and promote the iconic stature of these living monarchs and educate people about the key role that these remarkable trees and forests play in sustaining a healthy environment.

    Trees are ranked by total points based on the following formula: Circumference (in inches) + Height (in feet) + ¼ Crown Spread (in feet). The tree with the most total points is crowned national champion. The nomination deadlines are March and September 15th for the spring and fall registers, respectively. Dick's champion Hophornbeam has 210 points! I'll tell you how to measure your tree later in the post.

    The Eastern or American Hophornbeam - Ostrya virginiania if you're trying to impress Dick - is a member of the birch family of trees. Also known as ironwood, hardhack (in New England) and leverwood, it's generally a small short-lived tree scattered in the understory of hardwood forests. The tree is generally a subordinate species or minor member of most forest communities, when present. That's another unique aspect of Dick's champion - its unusually large size. Perhaps thriving in "the open" and Dick's nurturing nature has facilitated its large growth. 

    The Eastern Hophornbeam is a rugged, shade-tolerant tree with an oval or round canopy that grows to 50 feet in height. Dick's champion tops out at 66! It's found throughout the eastern United States and within the mountains of Mexico, south to El Salvador and Honduras. Over this large native range, it thrives in a diversity of climatic conditions and soils. Its small nutlets, which ripen in summer and fall, are used by birds and mammals during the winter. 

    It's often grown as an ornamental plant and sometimes used as a street tree. Because of its hardness, it has been used to make tool handles for mallets and posts. It should not be confused with the hornbeam, which is also a member of the birch family. The bark of a hophornbeam has loose strips of reddish brown to gray, creating a rough "clawed" bark.

    The hophornbeam's leaf is doubly-serrated with fine teeth at the margin and 2-4 inches long.

    I asked Dick what he knew of the age of his champion, it being slow-growing and having achieved such a large size. His best guess was about 135 years based on the age of his house. Dick speaks with the knowledge and ecological pride that comes from his BS in Forestry that he received from the University of Maine, although he doesn't pursue that profession, other than avocationally.

    Gazing up at the hophornbeam and shaking his head, Dick says that it has lost a good two-thirds of its crown, and that it wasn't registered until it lost the first third. "After losing the first third, no one would ever know that you have a champion. That's why I registered it. I looked up the previous champion - a tree in Michigan. The Commonwealth came to measure it near the end of 2008."

    Dick continued, "These types of trees are often culled early for pulpwood." Given its age and the deteriorated condition of its trunk, he fears that its days are numbered. "One good nor'easter, and that's it!" He's thought of cutting it down but is obviously highly reluctant.

    Even before I met Dick, I couldn't help but notice the tree as I jogged through the neighborhood. Maybe it was the signage that he proudly placed on the tree that caught my eye - one high and the other low. "Why the low signage?" I asked. "It's for the kids, and it's fun for everyone to read about it." Unfortunately, the bark that held the signs has rotted off, and they're now displayed on the logs.

    I was grateful for Dick telling me the story of his Eastern Hophornbeam and seeing his arboreal pride. He walked me back to my car, and quite sincerely added, "It's nice to find somebody that appreciates a championship tree!" And that I did! I must admit that I sneaked back the next morning to catch the morning sun illuminating its still majestic crown.

    1. Measure the distance around the trunk of the tree, in inches, at 4 ½ feet above ground level. This point is called the diameter breast height or dbh.
    2. If the tree forks at or below 4 ½ feet, record the smallest trunk circumference below the lowest fork. Record the height at which the measurement was taken. Trees should be considered separate if the circumference measurement below the lowest fork places the measurement on the ground.
    3. If the tree is on a slope, measure 4 ½ feet up the trunk on the high and low sides of the slope. The dbh is the average between both points. If the tree is on a steep slope, take the measurement at 4 ½ feet above the midpoint of the trunk.
    4. If the tree is leaning, measure the circumference at 4 ½ feet along the axis of the trunk. Make sure the measurement is taken at a right (90 degree) angle to the trunk.

    Measure the vertical distance, in feet, between the base of the trunk and the topmost twig. Height is accurately measured using a clinometer, laser, hypsometer, or other specialized tools.  If these tools are not available, height can be estimated using the following “stick method.”

    1. Find a straight stick or ruler.
    2. Hold the stick vertically at arm’s length, making sure that the length of the stick above your hand equals the distance from your hand to your eye.
    3. Walk backward away from the tree. Stop when the stick above your hand is the same length as the tree.
    4. Measure the distance from the tree to where you are standing. Record that measurement to the closest foot.

    Two measurements of the crown spread are taken and recorded, in feet, at right angles to one another.
    1. Measure the widest crown spread, which is the greatest distance between any two points along the tree’s drip line. The drip line is the area defined by the outermost circumference of the tree’s canopy where water drips to the ground.
    2. Turn the axis of measurement 90 degrees and find the narrow crown spread.
    3. Calculate the average of the two crown spread measurements using this formula: (wide spread + narrow spread)/2 = average crown spread.

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    Every blogger knows the challenge. What shall I blog about next? What photos should I use? By the time the end of the year rolls around, there are always a few posts that never quite made it. And so, with this final post of the year, here they are from here and there. Please visit the same for 2013 here and 2012 here.

    A Lustrous Pearl for an Illustrious New Year

    My wife and I ushered in the New Year with our traditional early dinner at a wonderful local restaurant. To our surprise, one of the saltwater oysters in her appetizer contained an opaque white, natural pearl - a one-in-a-million chance. 

    Pearls begin as foreign bodies within the mantle of a mollusk. The bivalve’s response is to secrete layer after layer of nacre (NAY-ker), a hard crystalline substance around the irritant for protection. The result is a pearl, which is similar in finish to the shiny inside of oysters and mussels, known as mother of pearl and can take 5 to 20 years to form (1 to 6 years for freshwater pearls). Light passing through the nacreous substance is reflected and refracted, which gives the pearl its luster and iridescence. This is because the thickness of the platelets of aragonite - a form of calcium carbonate (the other being calcite) - is close to the wavelength of visible light. Unlike gemstones that are cut and polished to bring out their beauty, pearls require no such treatment. 

    Finding a pearl is considered to be good luck, and looking back on this year, I would affirm that superstition. 

    William Smith’s Map That Changed the World

    "Sing, cockle-shells and oyster-banks,
    Sing, thunder-bolts and screw-stones,
    To Father Smith we owe our thanks
    For the history of a few stones."
    Anniversary Dinner by A.C. Ramsey, 1854.

    This eight by six-foot Delineation of the Strata of England and Wales with Part of Scotland is easily mistaken for a modern geologic map. Yet, it was created by William Smith in 1815 and was the first national-scale geologic map of any country covering 65,000 square miles. By far, it was the most accurate at its time and the basis for all others. Concealed behind stately green velvet curtains, it is on display in the foyer of the Geological Society of London’s Burlington House in Piccadilly alongside a bust of William.

    William Smith was born in 1769 in the hamlet of Churchill in Oxfordshire, the orphaned son of the village blacksmith. Raised by his uncle and with only a rudimentary education, he quickly learned the surveyor trade as an assistant. Fortuitously, he applied his skills with the Somersetshire Coal Canal Company, at which time he observed that rock layers within the canals were arranged in a predictable pattern and could always be found in the same relative positions. He also noted that each stratum was identifiable by the fossils that it contained and that the same succession of fossil groups from older to younger rocks could be found across the countryside, even as the layers dipped, rose and fell. In time, his astute observations led him to the hypothesis of the Principle of Faunal Succession – a major geological concept in determining the relative ages of rocks and strata. 

    Travelling throughout Britain, he observed exposures of the strata and meticulously sampled and catalogued their characteristics. First mapping vertically and then horizontally in color, his first sketch in 1801 led to the publication of the geological map of Britain. The timing was right. This was the dawn of the Industrial Revolution in England. Coal was king, and maps were needed. Yet, Smith's maps were plagiarized by the Geological Society of London, forcing him into bankruptcy and debtor’s prison. Destitute but not deterred after years of homelessness, Smith's bad fortune began to turn. 

    Over a decade later, he was eventually accepted into and honored by the Geological Society of London for his contributions as “the Father of English Geology.” In 1831, he was conferred the first Wollaston Medal by the Society in recognition of his achievements to the new science - all without a formal education in geology! It’s their greatest honor, bestowed by the very institution that denied him membership because of his low social status. Later, he was awarded an honorary doctorate of letters from Trinity College in Ireland. This uneducated surveyor rubbed elbows with famous astronomers, naturalists, biologists and geologists. 

    Simon Winchester in his book The Map That Changed the World summed up Smith's map as the work of a lonely genius. He states, "The task required patience, stoicism, the hide of an elephant, the strength of a thousand, and the stamina of an ox. It required a certain kind of vision, an uncanny ability to imagine a world possessed of an additional fourth dimension, a dimension that lurked beneath the purely visible surface phenomena of the length, breadth and height of the countryside, and, because it had never been seen, was ignored by all customary cartography. To see such a hidden dimension, to imagine and extrapolate it from the little evidence that could be found, required almost a magician's mind - as geologists who are good at this sort of thing know only too well today."

    The brilliance of William Smith’s achievement is demonstrated by comparing the accuracy and detail of his maps with the ones used by the Geological Society today and the rest of the world. His creation heralded the beginning of a new science and anointed him as its founding father. As for Dr. William Smith, nothing but goodness, recognition and respect attended the final years of his life.

    The Longitude Problem

    This is a High Dynamic Range photograph

    "The College will the whole world measure;
    Which most impossible conclude,
    And navigation make a pleasure
    By finding out the longitude.
    Every Tarpaulin shall then with ease
    Sayle any ship to the Antipodes."
    Anonymous (circa 1660) from the Ballad of Gresham College 

    On a foggy night in 1707, British Admiral Sir Cloudesley Shovell’s celebrated naval career was brought to a tragic end along with the lives of nearly 2,000 sailors, when his warship and three others in the fleet were wrecked on the rocks of the Isles of Scilly, off Great Britain's southwest coast. It was one of the greatest disasters at sea in British history and one of countless shipwrecks befallen to seafaring nations throughout history. The main cause of the British tragedy was the navigators’ inability to accurately determine their position at sea - longitude in particular. In response, Parliament established the Longitude Prize in 1714. The reward was for a "practical and useful" method for the precise determination of a ship’s longitude. The winner would collect £20,000 or roughly 4 million dollars in today’s currency, if accurate within half a degree (30 nautical miles at the equator). It was a large sum to pay for a desperate nation.

    Back in school, we learned that our planet is divided into an imaginary grid. Hula hoop lines of latitude or parallels encircle it horizontally, the largest at the equator, while vertical, equi-length, pole-to-pole lines of longitude or meridians mark locations east or west of the Prime Meridian or 0º longitude. Unlike the equator, the Prime's location is arbitrary and is a universally-accepted reference line whose location has varied historically (Until 1911, the French used a Paris meridian). As of 1851, it runs through the Royal Observatory at Greenwich, England, which is located on a majestic hill overlooking the Thames River, where the above photo was taken looking north. The line is actually slightly to the right, but 500 happy kids were busy straddling the line with one foot in each hemisphere. Used together, latitude and longitude provide every location on our earthly sphere with a global address, and when calculated, indicate one’s whereabouts on a map – an important feat at sea when land is out of sight. If you know where you are, then you know where you're going. Admiral Shovell would surely have agreed.

    One’s latitude is relatively easy to determine. Since ancient times, it was known that a star will consistently reach the same highest point in the sky, which changes with the observer’s latitude. By “sighting” the angle (declination) of the sun at it highest point from the horizon during the day or say the North Star at night, one’s position can be calculated from a table simply by knowing the time of measurement. On the other hand, finding longitude hasn't been so easy. Without it, ships at sea would follow a line of known latitude east or west, turn toward their assumed destination, and then continue on another line of known latitude. This process extended the voyage by days or weeks with increased risk of scurvy, bad weather, lack of potable water, starvation and worse - shipwreck. Another option was dead reckoning by using a predetermined “fix” and advancing that position based upon one’s known speed over time. Navigators threw a long, knotted rope overboard and counted the number of knots let out in a given interval to allow a distance and speed calculation. The process was subject to cumulative errors induced by wind, current and change of course.  

    The longitude problem was viewed by astronomers as requiring a celestial calculation such as by viewing eclipses of Jupiter's moons or our own, which required extensive heavenly observations and complex charts - hence the observatory in Greenwich. Clockmakers, on the other hand, envisioned the problem as requiring a temporal calculation. As expected from such a large reward, there was a myriad of hair-brained solutions such as a fleet of globally-distributed anchored ships that fired position-signalling cannons as longitude locators.

    Ultimately, it was John Harrison, a self-educated English carpenter and clockmaker, who, after over four decades of toil and experimentation, successfully invented a masterpiece of engineering. His H4 (earlier versions were H1 through H3) was a pendulum-less “sea clock” that was unaffected by movement and changes in temperature. At sea, a ship’s captain could, using Harrison’s marine chronometer, calculate longitude by comparing the time on his pocket watch to a constant clock at a predetermined location.  

    Here's how the the concept worked. The Earth makes a complete rotation on its axis every day. If there are 24 hours in a day, one hour of rotation is equivalent to 15º of rotation (360º ÷ 24). Thus, there exists a relationship between time and longitude. If you set your watch to 12:00 noon (not temporal noon but astronomical noon when the sun is highest in the sky at its zenith) at say Greenwich time, and you observe the sun at 4:00 PM at another location, then you’re at longitude 60º W (4 hours x 15º/hour = 60º). Finding local time was relatively easy. The problem was how to determine the time at a distant reference point while onboard a rocking, swaying, storm-tossed deck - an impossible task back in Cloudesley’s day with pendulum-swinging clocks that required a stable surface for accuracy.

    Harrison's H4, which basically looks like an over-sized pocket watch, achieved all that and more - pendulum-less, compact, portable, shipworthy and accurate. Harrison's many timepieces are on display at the Royal Observatory, and as for their inventor, he spent his final years tinkering and experimenting with many timekeeping innovations - a very wealthy man. 

    Plaster of Paris Meets the Father of Comparative Anatomy

    This is a High Dynamic Range photograph

    Built of gleaming white travertine (a redepositional form of limestone), the Basilica of the Sacred Heart radically changed the profile of the once pastoral, hilltop village of Montmartre - located on the northern outskirts of Paris and now an integral part of the city. Beginning in 1875, its 39-year construction was no easy task, since its foundation was literally riddled with subterranean gypsum quarries. 

    Gypsum- an evaporite mineral formed by dehydration in an arid environment - is used in the manufacture of Plaster of Paris by heating it and then reapplying water to get it to harden. It has been excavated from beneath Montmartre from antiquity through the 19th century. Amongst its many decorative and artistic uses, it serves as an effective natural fire retardant on wooden structures, akin to our modern plaster board. After the Great Fire of London in 1666, its use was decreed by French King Louis XIV and literally saved Paris from the destructive fires that ravaged all major European capitals. 

    The gypsum of Montmartre and the limestone of northern France formed within the Paris Basin. It began as an epeiric (shallow inland) sea on the northeastern fringe of Laurentia (the cratonic core of ancestral North America) some 200 million years ago. When the supercontinent of Pangaea fragmented apart beginning in the Late Triassic, the basin (and the new continent of western Europe) was tectonically transported to the Eastern Hemisphere on the Eurasian plate across an ever widening Atlantic Ocean. Once part of northern France, the basin’s sedimentary rocks of limestone and gypsum were deposited some 45 million years ago during the Lutetian Period of the Eocene. 

    Outspoken critics of the Sacre Cour project - not only because of its exotic architecture but its exotic ideology - feared a seismic outcome related to its enormous weight. The architect, who had been commissioned to build his design, thought an immense platform of concrete four meters thick would stabilize the structure over the quarries. Instead, 80 stone pilings were laid down through the lime and clay and deeper through the voids of the quarries until bedrock was struck over 30 meters down. In effect, the foundation of Sacre Cour rests upon stilts like a dock on pilings over water. If an earthquake was to strike Montmartre, after the dust settled some Parisians thought the edifice would remain intact as if floating in air. 

    When you visit Paris or on Google Earth, you can catch a glimpse of the entrance to one the quarries beneath the basilica fenced off on the northern end of rue Ronsard. It was in these very gypsum quarries that the famous French naturalist and zoologist Georges Cuvier excavated Eocene mammalian fossils from the strata in the 1790’s. His investigations led him to the inescapable conclusion that fossils were the remains of animals long-extinct. A lifelong Protestant, he believed that periodic catastrophies had befallen the planet and its lifeforms. That implied God had allowed some of his creations to vanish, a rather blasphemous conclusion against the tenets of the English church and one of the foundations of modern paleontology. Cuvier's contributions and uncanny ability to reconstruct lifeforms from their fragmentary remains led to his appellation as the “Founder of Comparative Anatomy.”

    The Seine's Epic Journey to the Sea

    Four large rivers water France – the Loire, the Seine, the Rhine and the Rhone – linked by a system of interconnecting canals. The second longest is the Seine (pronounced SEN), which begins a 776 kilometer (482 mile) journey to the sea from a modest cluster of springs called the Source de Seine northwest of Dijon. This is the Cote d’Or, literally “golden slope” that arguably produces the best wines (and mustards) in the world. It’s the right combination of climate, soil, and of course, clean water. 

    The Seine flows through a thousand tiny hamlets, fields and woodlands, and halfway to the sea, right through the middle of Paris. It divides the city into its two famous banks - the conservative Left Bank or Rive Gauche and the radical Right Bank or Rive Droite. The Seine is the heart and soul of Paris, where the Parissi tribe first settled and where Romans took residence in their conquest of Gaul in 52 BC. 

    The Seine flows through an enormous geological depression flanked by huge escarpments that began to flood when it was part of an intricate network of inland seas when the Atlantic Ocean was just beginning to open. The supercontinent of Pangaea’s fragmentation sent the Paris Basin adrift on the Eurasian Plate across the Atlantic Ocean, along with a network of interconnecting basins in western Europe. Good thing for France. The River Seine is actually a recent waterform within the ancient trough, having originated when the Pleistocene ice sheet and enumerable alpine glaciers sent their waters to the sea from the highlands that encompass the basin. 

    Twenty-six tributaries later, the estuarine Seine discharges into the ocean, more precisely the English Channel, between the twinports of Honfleur and Havre, seen above through the clouds.

    Blue Skies, Green Water and Red Rocks on the Stove Pipe Trail

    “The landscape everywhere, away from the river, is rock – cliffs of rock; tables of rock; 
    plateaus of rock; terraces of rock; crags of rock – ten thousand strangely carved forms."
    John Wesley Powell, 1875

    Originating in the Wind River Mountains of Wyoming and skirting the northwest corner of Colorado, the Green River flourishes in Utah in all its glory. It's a 730-mile long, chief tributary of the Colorado River before reaching their confluence at the southern terminus of the Island in the Sky. In northeast Utah, the Green carves its channel over and through fluvial and marine rocks of Cretaceous age - grayish remnants of a vast inland sea that connected then-warm Arctic waters with those of the Gulf of Mexico, yet to form. In southeast Utah, things change dramatically, as the river downcuts through rocks of Jurassic, Triassic, Permian and Pennsylvanian origins.

    This is Canyonlands, where John Wesley Powell in 1869 surveyed, mapped, described and named the landforms on the first of two expeditions to the region. First, through curvy Labyrinth Canyon and then more linear Stillwater Canyon, both appropriately named, the Green River slices its way back in time through confining cliffs of the Jurassic Glen Canyon Group and underlying erodible slopes and ledges of Triassic Chinle and Moenkopi Formations. The strata of these two geologic periods of the Mesozoic tell a tale of widespread Jurassic aridity in western Pangaea and distant Triassic mountain ranges draining across vast floodplains and river systems to the sea.

    Our journey down the Green River - under the leadership of famous geologist Wayne Ranney and the supreme navigational skills of Walker Mackay and his family-run Colorado River and Trail Expeditions or CRATE - rafted us into camp at the foot of the Stove Pipe Trail in Stillwater Canyon, about seven miles upriver from the confluence. 

    To work up an appetite for dinner, we ascended over 1,000 feet through a series of switchbacks and a palette of colors derived from cherty, chalky limestones and dolomites, pale-red sandstones, blue-gray siltstones and thin beds of evaporites of the Elephant Canyon Formation. At the top, where the photo was taken, the white to pale-reddish brown and salmon-colored Cedar Mesa Sandstone comes into view, forming the cliffs and ledges that hold it all up. These Permian strata are derived from the Ancestral Rocky Mountains or, more appropriately, the southwest range of the Uncompahgre Highlands that began their ascent in Pennsylvanian time. As they rose, the inexorable forces of erosion tore them down. Here too was an inland sea represented by the Uncompahgre's flexural trough that persisted with intermittent communications with the ocean and whose dimensions vacillated with the whim of South Polar glaciation an astounding 33 times. To see the strata within the trough, we had to wait for the following day in order to travel further down the Green. 

    Both long gone, the highlands and basin left their signature deposits from Colorado to Utah. Uplift and erosion of the Colorado Plateau have put the finishing touches on the landscape. What's left is a rainbow feast for the eyes!

    Born to Reproduce

    On a glorious Spring afternoon outside of Boston, I exited the train station and began the short walk home. A bright colored object on the ground caught my eye, and, glancing down, I spotted this splendid Cecropia Silkmoth (si-KROH-pee-uh) on the pavement. A little worse for wear, I photographed it with my cellphone. I recognized the creature, having remembered a pinned specimen from sixth grade biology class so long ago. 

    The cecropia is North America’s largest moth and are abundant east of the Rockies, although this specimen is the first I’ve seen outside of class. Females achieve a wingspan of seven inches! The larvae are mostly found largely on maple trees, which squirrels fastidiously dine on. I suspect this is a male, based on the more resplendent morphology of its antennae, having evolved as such for one specific purpose. 

    Born to reproduce, nocturnally-active males lack functional mouthparts and a digestive system, and therefore survive only a few weeks. Unable to resist, males fly miles following the scent plume of wind-born female pheromones, guided by their antennae. Using an adaptive process called chemical mimicry, bolas spiders copy the pheromones produced by cecropia females, in order to lure males into their next meal. Predators and their prey exist up and down the food chain at virtually every level.

    Architectural Geology of Boston – the Oldest Cut Granite Building in America

    "In the love of truth, and the spirit of Jesus Christ,
    We unite for the worship of god and the service of man."
    King's Chapel Covenant

    King’s Chapel in Boston was designed by Peter Harrision of Rhode Island and built in 1754 on the site of a smaller wooden Anglican church, itself built in 1688. It was situated on the public burying ground, because no resident would sell land for a non-Calvinist church. The stone church was constructed around the wooden church, so that the parishioners could continue to practice their faith, and was later disassembled and removed through the windows of the new church. 

    The edifice is a classic example of American Georgian architecture – eponymous for the first three British monarchs of the House of Hanover, all named George in the early 18th and early 19th centuries. Its salient architectural features include a tall, boxy portico surrounded by 12 painted Ionic columns made of wood. The cornice has decorative mouldings and is topped off with a spindled-balustrade that terminates in a flat-roofed tower with four louvered, arched windows. The planned steeple was never built, which gives the church its distinctive "unfinished" look. Directly behind, the chapel has a characteristically four-sided, hipped roof. The Georgian style was big in eastern America, that is until King George III and the American Revolution turned the aesthetic sentiment elsewhere.

    King’s Chapel was originally planned to be of English sandstone but was built with native Quincy Granite. It's the oldest, still-standing granite building in Boston but not the first to utilize granite, having been incorporated into many early foundations and associated structural elements. The blocks of granite demonstrate a patchwork color mix with pockmarked surfaces on the exposed “seam-faces.” 

    The granite's appearance is reflective of the mode of quarrying from boulders scattered about rather than from excavated bedrock. The process involved heating and splitting the granite with heavy iron balls, followed by hammering, chiseling and shaping into stackable units. The "quarry" locale was Quincy (pronounced KWIN-zee), about 10 miles south of Boston. The town is officially called the “City of Presidents” after John Adams and John Quincy Adams, but its nickname is the Granite City. A hundred years later, the use of famous Quincy Granite in construction would become commonplace in Boston, and quarrying the bedrock would become a major commercial enterprise there.

    By the way, in the bowels of King's Chapel is a 200-year old crypt and in the tower is the largest and last bell made by Paul Revere. It's located on the famous Freedom Trail, the red brick line on the pavement in front of the chapel.

    The Granite Railway

    In the face of great opposition to his idea, architect and engineer Solomon Willard traipsed all across New England looking for the perfect stone. His plan, after several architectural modifications, was the construction of a 221-foot tall obelisk out of Quincy Granite - the Bunker Hill Monument - situated in Charleston across the harbor from Boston. By comparison, the Washington Monument - built to commemorate George Washington - was completed in 1884 on the National Mall in Washington, DC, and is the world's tallest stone obelisk at 555 feet. Willard's edifice was built to commemorate the Battle of Bunker Hill, the first major conflict between the British Regulars and the Patriot forces of colonial militiamen in the Revolutionary War fought in 1775. Technically, the monument is not on Bunker Hill but on Breed’s Hill, where most of the fighting in the misnamed Battle of Bunker Hill actually took place.

    In 1825, Willard recognized there was something special about the granite in the hills west of Quincy. It wasn’t its convenience, since the granite still had to be excavated - no easy or safe task back then. It wasn’t its proximity (although that helped), since a lot of varied terrain stood in the way of the granite’s final destination. And it wasn’t the granite’s massivity - not meaning lots of it (which there was) but referring to its consistent homogeneity for aesthetic purposes. 

    It was from Quincy Granite’s unique mineral composition. The high percentage of alkali feldspar, as opposed to the plagioclase variety, affords the rock its dusty gray, greenish tint, aided by its variety of black quartz. Formed from the slow crystallization of magma some 450 million years ago when the micro-terrane of Avalon was in transit to Laurentia, the granite’s characteristic mineral of riebeckite, a brittle prismatic amphibole, allows the rock to achieve a high polish, in addition to its lack of micas. Quincy Granite was the rock that Willard sought - attractive, distinctive, stately, transports well, available, highly polishable and weather-resistant. 

    However, a major obstacle in 1826 was getting multi-ton blocks out of the ground, down from the heights above Quincy and across 12 miles of swamp, forest and farms for construction. After considering an overland route, the solution of how to transport the blocks from the quarry to a dock on the Neponsett River was modeled after English railroads. The idea for the Granite Railway was conceived and became not the first public transportation railroad in the United States but the first purpose-built, commercial railroad. 

    It ran only three miles with wagons pulled by horses, although steam locomotives had been in operation in England for two decades. Wooden and later granite rails on stone crossties were plated with iron. In 1830, a new section of railway called the Incline, seen above, was added to haul granite from the quarry, one of many above town. Wagons and horses moved up and down the 315 foot incline in an endless conveyor belt. From the docks, blocks were loaded on barges that traveled across Boston Harbor. Off-loaded onto ox-drawn carts, the cargo went up a hill at Charleston for construction of the obelisk. The capstone was laid in 1842 at a project cost of $101,680. Interestingly, the monument underwent a 3.7 million dollar renovation in 2007 - the cost of 36 monuments!

    The Incline remained in operation until the 1940’s with metal channels laid over the old granite rails and motor trucks pulled by a cable. In 1871, steam trains carried the granite directly to Boston from the quarries.

    These days, the quarries have been filled in for safety purposes with 12 million tons of dirt from the Big Dig highway project in Boston. In years past, many young persons were injured or killed while swimming and cliff diving into the abandoned quarries that had filled with water. Ironically, the steep quarry walls are used today by organized groups of rock climbers to hone their skills. As for the Granite Railway, it's listed on the U.S. National Register of Historic Places, while the Bunker Hill Monument towers over Charleston across the harbor from Boston proper. You could see it from the quarry, if it wasn’t for the city's tall buildings. The Bunker Hill Monument is managed by the National Park Service and is on Boston’s Freedom Trail. 

    The Bridge that Spans Two Geologic Eras

    Viewed from Upper Manhattan, the George Washington Bridge spans the Hudson River between New York and New Jersey. Its footings are secured in two geologic eras. Cross the bridge heading west, and you time-travel from the Late Proterozoic to the Paleozoic. During the Late Triassic, the supercontinent of Pangaea began its fragmentation and newly-evolving dinosaurs were trudging through the mudflats of the Jersey Meadowlands. That epic schism created the continents of our New World and the Atlantic Ocean within the void, while the North American and Eurasian tectonic plates continue to drift apart. 

    During supercontinental breakup, aborted rift basins from the Canadian Maritimes to Georgia developed up and down the margin of North America. In northeastern New Jersey and southeastern New York, the Newark rift basin subsided and listrically tilted as molten mafic rocks injected through the depocenter’s sedimentary strata into black argillites of the Lockatung Formation. The prominent cliff seen above on the western bank of the Hudson represents the eroded edge of that angulated, tabular intrusive sheet – the famed Hudson River Palisades. Its obvious vertical jointing formed when the magma solidified, so spectacularly exposed by the carving of the Hudson Canyon during the last Ice Age. 

    The Palisades was threatened by quarrying in the early 20th century, when J.P. Morgan, American financier, banker, philanthropist and art collector, purchased twelve miles of New Jersey shoreline. On the east side of the river in Washington Heights, John D. Rockefeller, American business magnate and philanthropist, acquired the land of Fort Tyron and the Cloisters, where this photo was taken. 

    Thankfully, the natural beauty of the Palisades cliffs rising above the west bank of the Hudson has long been appreciated by generations of residents and visitors to the metropolitan area. But now, LG Electronics, a South Korean multinational electronics corporation, is planning to build an office tower that will rise high above the trees, and for the first time, violate the unspoiled ridgeline. Interested in preserving the Hudson River Palisades? Visit “Protect the Palisades” here.

    That's all folks. Thanks for following my blog! Happy New Year!

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    "At first it may seem to be a piddly little dribble through the farmlands and forests of rural New Jersey, 
    but careful observation shows Monmouth County's Big Brook 
    to be glass-bottomed boat sailing through a Late Cretaceous sea busy with life.” 
    From the New York Paleontological Society Field Guide, 2002

    Big Brook at a slightly high water level as seen from the Hillsdale Road bridge facing east

    Step into the waters of this very ordinary-looking brook, and you’ll go back in time to North America’s continental shelf only a few million years before the Great Extinction that ended the Age of the Dinosaurs. In its lazy and short course to the Atlantic, Big Brook has carved a shallow, curvy trough through New Jersey's Inner Coastal Plain through the upper sediments of a Late Cretaceous paleoshelf. In so doing, weathering of the streambank provides a steady supply of fossils that are washed into the streambed.

    Big Brook is one of the East Coast’s classic fossil-collecting localities with both amateurs and professionals alike. As early as 1863, the Smithsonian Institute in New York sent an expedition to explore and gather fossils from the brook and others within Monmouth County. Less widely appreciated amongst amateurs is that the strata through which Big Brook transects preserves an outstanding sedimentological record of the transition from an inner to an outer shelf environment during the Late Cretaceous as sea level rose.  

    Although rare, be on the lookout for fragmented, water-worn dinosaur bones and teeth - hadrosaurs, theropods, ankylosaurs and ornithomimids - from the Late Cretaceous terrestrial shoreline to the west. Add to the mix, Pleistocene mammalian remains of mastodon, sloth, beaver and horse. From the Holocene, there's even an occasional Native American Lenni-Lenape arrowhead from the surrounding countryside and a coral from Paleozoic tropical seas entrapped within the Appalachian orogen that was transported to the area fluvially or via glacial outwash.

    A Late Cretaceous terrestrial fauna similar in some respects to eastern North America
    From National Geographic

    But by far, the big attraction is teeth from Late Cretaceous chondrichthyans (shark, rays and skates) and, less often, osteichthyans (bony fish) and large marine reptiles (mosasaurs, turtles and plesiosaurs). 

    The Late Cretaceous marine ecosystem teemed with life. 

    In addition, abundant macro-invertebrate remains include brachiopods, bryozoans and molluscs (bivalves such as oysters, snails, belemnites and ammonites) and disarticulated arthropod carapaces and claws (lobster, crab and shrimp), all from the Late Cretaceous shelf ecosystem. 

    The shelf's benthic and demersal zone was rich and diverse with brachiopods, bryozoans, molluscs and arthropods.
    From Matthew McCullough on Flickr and license here.

    Big Brook is barely 50 miles south of New York City via the Garden State Parkway off exit 109 west. The brook winds its way through the rural New Jersey hamlets of Colts Neck and Marlboro to the Navesink River near the borough of Red Bank, and ultimately the Atlantic Ocean. Besides Big Brook, other nearby fossil-bearing tributaries include Poricy Brook in Middletown Township, Ramanessin Brook in Holmdel and Shark River (Eocene and Miocene) in Neptune and Wall Townships. They're all located in gentrified and well-healed Monmouth County, which is in the top 1.2% of counties by wealth in the United States. The County's website advertises itself as the "Gateway to the Jersey Shore", while locals know it as Springsteen country (“…sprung from cages on highway nine…”). 

    The arrow points to the location of Big Brook within Monmouth County.
    Modified from Roadside Geology of New Jersey

    Some sixty-seven million years ago, this lazy, oak-shaded stream and the surrounding countryside were a tiny submerged section of the newly-formed, Atlantic continental shelf. During the Late Cretaceous, global high seas drowned the shelf that now represents the broad, low relief of the Atlantic Coastal Plain through which Big Brook flows. But the geological story of the plain begins well before the Cretaceous. 

    Paleozoic tectonic convergence...
    Beginning in the early Paleozoic, Laurentia - the rifted megacontinental sibling of the Late Proterozoic supercontinent of Rodinia - was converged upon by a procession of magmatic arcs, micro-continents and megacontinents and their intervening ocean basins. 

    Birth of Pangaea...
    In a parade of orogenic events, they accreted to Laurentia's growing ancestral core - building mountains and adding crust with each collision. By the Pennsylvanian Period of the Paleozoic (below), their cumulative convergence had constructed the supercontinent of Pangaea and built a massive, centrally-located mountainous spine. By the Late Permian at the close of the Paleozoic, the mountains had been ravaged by erosion.

    Subsequent to the collision of Gondwana (the other megacontinental sibling of Rodinia) with equatorially-positioned Laurentia in the Middle Pennsylvanian, Monmouth County is nestled somewhere within the lofty peaks of the Appalachians. The supercontinent of Pangaea is fully formed and awaits its imminent fragmentation.
    Modified from Ron Blakey and Colorado Plateau Geosystems. Inc.

    Demise of Pangaea...
    In the Late Triassic, Pangaea’s fragmentation began. As the Atlantic Ocean began to open within the schism, the remnants of Pangaea's central mountainous spine began to fragment as well. A portion remained astride the Atlantic Coast in newly-formed eastern North America - today's Appalachians - while other remnants were carried across the globe on the backs of Pangaea's rifted siblings. Pangaea's breakup also endowed North America (and of course New Jersey) with a new passive shoreline characterized by seismic and volcanic inactivity, and most importantly, subsidence and sedimentation. 

    Subsidence and sedimentation of the Atlantic margin...
    Beginning probably during Jurassic time, lithospheric cooling of North America's newly-formed passive margin, in concert with the weight of voluminous sedimentation, promoted rapid subsidence and provided a vast accommodation space for the accumulation of clastic erosive products. With subsidence, the Atlantic margin was broken into a series of faulted-blocks, which experienced differential movements. 

    Downward movement created embayments - deep indentations of the ancient shoreline in which sediments accumulated in greater thicknesses in greater water depths. Upward movement created structural highs, arches or uplifts - with thinner sequences and even the absence of deposition. One such coastal geo-indentation that would become a portion of the Coastal Plain - the Raritan embayment - influenced sedimentation in New Jersey between Staten Island at the western end of Long Island and Jersey's northern Coastal Plain.  

    Map showing the outline of the Atlantic Coastal Plain and major structural elements that persist on North America's modern coast line. In particular, the Raritan Embayment between is encircled.
    Modified from Summary of Lithostratigraphy and Biostratigraphy of the Atlantic Coast by Ollson

    Formation of the Atlantic Coastal Plain...
    Concomitant with crustal cooling and subsidence, deposition in the coastal plain began in earnest in the Early Cretaceous with fluvial sedimentation from the highlands of the Appalachians. However, in the Late Cretaceous (below), marine incursions representative of global high seas flooded low-lying regions of the world that included the newly-formed, low-lying Atlantic coast.

    Progressing from the shoreline seaward, gravel and sand on the inner continental shelf gave way to silt and clay, and, in progressively deeper water, glauconitic sand and silt. The deposits record a progressive but discontinuous and fluctuating rise in sea level - perhaps four in Late Cretaceous time and three in the Cenozoic. Thus, the landform of the Atlantic Coastal Plain gradually developed, representative of some 150 million years of sedimentation.

    Of course, the flood waters of the Cretaceous have receded exposing the broad Coastal Plain on the eastern seaboard. Although global seas continued to vacillate, erosion became the dominant geological process through the Tertiary. Ice Age glaciers made it to northern New Jersey but not to the south, while the Coastal Plain continued to receive a thin and varied veneer of colluvial and alluvial Quaternary and Holocene debris. Today, the modern shoreline is 10 miles to the east of Big Brook as it lethargically dissects its way to the sea through Late Cretaceous sediments. 

    With Pangaea fragmented apart, the Late Cretaceous witnessed the initiation of the development of the ecosystem of Monmouth County (red dot) on the submerged Atlantic Coastal Plain (light blue). The Atlantic Ocean has opened between the north and south, and is actively spreading. Note the Mid-Atlantic spreading center (light blue) along the line of tectonic divergence. The Western Interior Seaway in central North America is about to become confluent between the waters of the Arctic and the Gulf of Mexico.
    Modified from Ron Blakey and Colorado Plateau Geosystems. Inc.

    The Paleozoic collisions that assembled North America formed geomorphic provinces that are seen in the colorful mosaic of the Tapestry of Terrain and Time map by the USGS here. The yellow and tan Cretaceous and Cenozoic deposits of New Jersey (within the ellipse) illustrates the extent of the Coastal Plain within the state, which is continuous with that of the entire Atlantic and Gulf Coasts from Cape Cod and Long Island, through northern Jersey at Sandy Hook to southern New Jersey at Cape May, and down to Florida and around to the Gulf of Mexico. Let's take a closer look at the provinces of New Jersey.

    The geomorphic provinces of Northeastern and Mid-Atlantic North America with New Jersey encircled. 
    Modified from the USGS Tapestry of Time bedrock map located here.

    For an area its size, New Jersey has a diverse geological history. From west to east, from the mountains to the sea, and across the multitude of orogens that formed eastern North America, New Jersey’s main geological subdivisions or provinces are the Valley and Ridge, the Highlands (equivalent to the familiar Blue Ridge down south), the Piedmont and the Coastal Plain

    By definition, the four geomorphic or physiographic regions are each unique as to relief, landforms and geology. Being inherited subsequent to the tectonic collisions that occurred throughout the Paleozoic, they're on strike from northeast to southwest in accordance with the direction of tectonic convergence. A fifth smaller province - in accordance with tectonic divergence - is the Newark Basin (green and red), which lies interposed within the Piedmont. It's a sediment-filled rift-basin, one of many along the east coast that formed during the initial stages of Atlantic opening in the Late Triassic and Jurassic.

    Geologic Bedrock Map and Physiographic Provinces of New Jersey
    The region of Big Brook within the Atlantic's Inner Coastal Plain is located at the red dot.
    Modified from the Department of Environmental Protection, Division of Science, Geological Survey, 1999

    The Coastal Plain Province is relatively featureless, save a few gently undulating hills, and overlaps the rocks of the Piedmont Province to the west. It covers the entire lower half of New Jersey (see above map), dipping seaward from 10 to 60 feet per mile to the the southeast and extending beneath the Atlantic Ocean to the edge of the Continental Shelf at the Baltimore Canyon Trough. Its unconsolidated and compacted (but not cemented) sediments range in age from the Cretaceous to the Miocene. The composition of its bedrock and fossils confirms that it was submerged by Late Cretaceous high seas. 

    This west to east cross-section through the modern Coastal Plain and continental shelf illustrates the increasingly deep seaward-facing wedge of sediments that extends from a feather edge at the Fall Line of the Piedmont to the sea, where it's over a mile thick.
    From the USGS and the Roadside Geology of New Jersey

    The Coastal Plain is further subdivided into two regions. Because it was uplifted, weathered and dissected, the Inner Coastal Plain is higher in altitude than the Outer Plain but not by much. Its composition is largely a mix of quartz sand, glauconitic sand, silt and clay. This fertile agricultural zone gave rise to New Jersey’s nickname as the Garden State. It's also the location of Big Brook within Monmouth County. The Outer Plain is a region of lower altitude where low-relief terraces are bounded by subtle erosional scarps. It consists of Tertiary and Quaternary sand, and being acidic and less fertile, is the location of Jersey’s heavily forested cedar swamps and pine-scrub oak of the Pine Barrens. 

    As mentioned, in the Early Cretaceous the Coastal Plain region of New Jersey received deltaic and floodplain-derived (non-marine) sediments from the Appalachian highlands to the west. In the Late Cretaceous and into the early Paleocene, sea levels rose and flooded the coastal region in a series of transgressions over land and regressions back again. Layer after layer, sequence after sequence (packages of strata deposited during a single cycle of sea level rise and fall), sediments of the sea were laid down beginning with the earliest Late Cretaceous Raritan Bass River Formation upon the latest Early Cretaceous fluvial Potomac Formation (chart below). 

    In the late Late Cretaceous - from the Campanian into the Maastrichtian - the Monmouth Group, the state's youngest Cretaceous package, was laid down - a unit that is compacted but unlithified. New Jersey's Monmouth Group includes the basal Mount Laurel sand (5-60 feet thick), the transgressive marl of the Navesink (25-60 feet thick), the regressive silt and sand of the Redbank Formation (thin film to 100 feet thick) and the Tinton Formation's coarse quartzose and glaucontic sand (20-40 feet thick). 

    As the sea transgressed and regressed, shorelines moved accordingly. Existing sediments were eroded, reworked and redeposited, leaving behind unconformities. Breaks between sequences were punctuated by lag deposits or "shell beds." The great majority of fossils at Big Brook such as within the Navesink Formation, which we will visit, were eroded from lag deposits and released into the streambed. They were deposited within the neritic zone - the relatively shallow waters of the ocean from the littoral zone (closest to the shore) to the drop-off at the edge of the continental shelf. 

    Big Brook's journey to the sea, has excavated a channel into the Inner Coastal Plain. It cut through the Red Bank Formation's Sandy Hook Member (Krsh), through the Navesink Formation (Kns) and underlying Mount Laurel Formation (Kml), and in some areas, into the Wenonah Formation (Kw) - all deposits of the vacillating Late Cretaceous sea. You can find the complete map of the Freehold and Marlboro Quadrangles here. For orientation, the red arrow marks the location of the car park on the north side of the Hillsdale Road bridge. 

    This map depicts the channel of Big Brook. The red arrow points to the car park on the north side of the Hillsdale Road bridge.
    Modified from the Bedrock Geologic Map of the Freehold and Marlboro Quadrangles, New Jersey, 1996.

    Two unmarked bridges are your portals to Big Brook- one on Boundary Road and the other on neighboring Hillsdale Road just east. On the north side of the Hillsdale Road bridge is a designated car park, while parking is on the street just south of the Boundary Road bridge (as of this writing). The photographs taken and fossils displayed in this post were from four visits to Big Brook on the east side of the Hillsdale Road Bridge. 

    The countryside through which Big Brook flows is peppered with residential settlements, horse farms and wineries that are either private or post no trespassing. Big Brook's banks are private as well and off limits to excavation. They're dangerous too, since they are unconsolidated and slump and collapse with little provocation, especially by overzealous excavators. But the streambed is fair game. The only caveat is that on a nice summer day you may have to share it with a paleontologist, a geologist, a scout troop and a fossil club - all after the same piece of time.

    The bucolic Hillsdale Road bridge over Big Brook facing south

    To extract the fossil bounty at Big Brook Preserve, no geological hammers and chisels are necessary owing to the unconsolidated nature of the bedrock. In fact, they're prohibited by a posted Colts Neck Township ordinance in order to preserve the resource and minimize over-collecting. All you'll need are a pair of Wellies or suitable waders (there's some broken glass so don't go barefoot), and equip yourself with a garden trowel (with a maximum blade length of 6") and a small, homemade sifting-screen (no greater than 18” x 18”). I borrowed a kitchen colander from home. 

    The Department of Recreation and Parks of the Township of Colts Neck has determined that "there is an increasing need for the preservation of the many natural resources located within Big Brook Preserve. It has been observed that natural resources such as fossils have been taken from the park in large quantities. It has also been observed that certain other dangerous conditions continue to threaten the natural beauty, assets and environmental resources within Big Brook Park." 

    Therefore, "Fossil extraction is prohibited from the walls of the streambed above the stream waterline", and "No person may harvest more than five fossils per day." With all that in mind, you’re ready to “beachcomb” at Big Brook, panning and sifting for treasures buried within the streambed.

    After parking your car in the designated area, assemble your regalia, and follow the short footpath through the woods on Late Cretaceous Navesink soil. You can make out the brook's shallow, shady trough running from right to left. I've been to Big Brook many times over the years and haven't seen one mosquito or tick. Having said that, come prepared! 

    The short path through the woods to Big Brook

    Slide down the vegetated slope to the brook, and step back in time into the continental shelf. The deposition rate of the Navesink has been estimated to be about a meter in a million years, so from the footpath to the streamline, you're back about 2 million years. You can wade through the brook upstream (west) to the Boundary Road bridge about a half-mile or go downstream for a quarter-mile or so.

    The Hillsdale Road bridge seen from Big Brook. 
    The water level is somewhat high here, so the mudflats would be the best option for fossil-foraging.

    Within the brook's oak-shaded world, things become quiet and peaceful with gurgling waters, chirping birds, occasional hawks cruising overhead and gentle breezes wafting down from above. Only the occasional car flying across the bridge will remind you of the civilization that surrounds you. 

    Many collectors choose to visit Big Brook in the Spring or after a heavy rain, thinking that new runoff refreshes the fossils that weather in from the banks. Others say it makes no difference. Cobbles and fossils tend to aggregate in horizons, so many collectors focus on sieving there. 

    If the brook is at high water and the bed is totally flooded, it's safest not to enter, besides, hunting for fossils will be extremely difficult and unproductive. Trees and large limbs that have fallen across the brook add a measure of challenge to negotiating the stream, especially if the current is swift and you're forced to the center of the channel.

    Seen here at high water, the brook's bed, gravel bars and mudflats are less accessible for foraging. 

    Wade and trudge around until you've found a "good" spot, be it a mudflat or gravel bar, or simply excavate directly into the streambed. Just don't disturb off-limit streambanks. Although highly fossiliferous and tempting, once again, they are unstable. Groundwater near the base of exposures is under artesian pressure and continually discharging from small seeps and springs that undermine the cliff-face provoked by the slightest excavation - historically a potentially fatal mistake.

    The stretch of brook east of the Hillsdale Road bridge is largely within the Navesink Formation, while portions of the bed are in the Mount Laurel and deeper Wenonah. The age of the Navesink has been estimated to range from about 70 million years at the base of the formation to about 66 million years at the top, almost at the end of the Mesozoic. 

    By the way, above the Tinton Formation of the Monmouth Group, the K-T boundary between the end of the Cretaceous and the beginning of the Cenozoic ("T" stands for Tertiary) has been identified in test borings beneath the Outer Coastal Plain and at Inversand Mine in the town of Sewell within the Inner Coastal Plain on the western part of the state across the Delaware River from Philadelphia.

    The Navesink is a transgressive interval in the last of six depositional cycles of changing sea levels coupled with subsidence that includes the overlying Red Bank formation. An idealized cycle includes a basal glauconitic unit (of massive flooding and maxiumum faunal diversity), a superjacent clay or silt surface (representing the highstand tract deposited in shallower water than the previous tract), and a sandy unit (that may contain a lowstand tract at the top). The sequence of lower glauconite sand, middle clay-silt and an upper quartz sand was repeated some four or five times on the plain's inner to mid-shelf in the Late Cretaceous.

    Glauconite sands of New Jersey...
    The Navesink is a massively bedded, olive-gray, olive-black and dark greenish-black clayey, glauconite sand unit - also called greensand or marl - that is compacted but unlithified. Glauconite is an iron-rich mica (iron potassium phyllosilicate) that forms diagenetically at the sediment-water interface on the continental shelf from clay minerals during prolonged intervals of sediment starvation. Glauconite is not confined solely to the Navesink but is found in most of the Late Cretaceous formations within the Inner Coastal Plain. 

    Geologic bedrock map of Late Cretaceous and Paleogene Formations of New Jersey's Inner Coastal Plain
    Modified from Zehdra Allen-Lafayette

    The coastal plain's glauconite beds are not only highly fossiliferous but, being nutrient-rich and holding water, were widely mined as fertilizer in the 19th century. In fact, the duck-billed dinosaur Hadrosaurus foulkii was discovered in an old marl fertilizer pit in Haddonfield, New Jersey, in 1858. It was the first almost complete dinosaur skeleton discovered in the United States and is now the New Jersey state fossil. The hadrosaur, being terrestrial as all dinosaurs, was thought to have been carried to the plain's former marine environment via a "bloat and bloat" or "fluvial-flood carried" scenario. The time-frame and curious marine burial are reminiscent of the therizinosaur Nothronychus graffami in Big Water, Utah. You can read about it in my post here.  

    Highly fossiliferous and bioturbinated...
    Big Brook's banks provide an excellent opportunity to inspect a portion of the Navesink in cross-section down to the streamline. Above the Navesink are fossil-depauperate sands of the Red Bank Formation, stained red by iron oxide. Within the Navesink are quartz-rich sand layers and sand-filled burrows containing granules, black phosphate pebbles and small lignite fragments. Unseen are planktonic microfossils (such as Globotrucana gansseri and Lithraphidites quadratus), and, to the unaided eye, disarticulated macrofossil horizons of bivalves

    The latter form lag deposits exposed within the streamcut that are traceable for some distance. Lag deposits are common in the Late Cretaceous of North America and represent complex taphonomic histories that include multiple episodes of exhumation and reburial associated with sea level cyclicity. Although a work in progress, four or more distinct facies within the Navesink have been identified using these litho- and biofacies horizons that correlate to sequence boundaries and unconformities.  

    Standing directly in Big Brook's stream, this cut bank is within the Navesink Formation with a portion of the overlying Red Bank Formation. The voids are where large clusters of bivalves have avulsed (or were excavated) from the glauconitic matrix. 

    Iron-rich mineral seeps help to identify bedding interfaces. Note the myriad of overlapping vertical and horizontal burrows exposed within the bank. The extensive infaunal bioturbination is very evident. Not one visitor to Big Brook that I've seen has taken the time to study the streamcuts through the Navesink. There's a great story to be told in the banks, not just by what's washed into the bed!

    Close-up of a heavily bioturbinated and water-saturated Navesink bank with an iron-rich mineral seep.

    The fossil fauna of Big Brook is in keeping with a thriving shelf environment. The following is a small sample of its bounty discovered on four visits to the brook east of the Hillsdale Bridge. 

    It's easy to overlook small fossils from the brook's mud and gravel bed, especially tiny shark and fish teeth, some of which are a barely 2 mm in diameter. The screen affords an opportunity to patiently inspect your excavated sample. Note the camouflaged remnants of a Gyrphaed scallop shell, a Cephalopal belemnite rostrum and a Squalicorax shark tooth below.

    A gravel bar alongside the streambed of Big Brook

    Unquestionably, the major attraction at Big Brook is shark teeth, and there are many varieties to be found. To the geologically-uninitiated, they appear incongruous to the modern landscape. Their abundance is a testimony to the richness of the Late Cretaceous ecosystem. 

    Shark teeth are well preserved, whereas their skeletal remains being cartilaginous are not, with the exception of an occasional vertebral centrum. All the dental specimens, particularly the radicular structures, being less calcified and more porous, are stained by iron derived from the host sediment. Some permineralization of the teeth has occurred during burial, fossilization and diagenesis (alteration induced by chemical and physical processes mediated by water and stopping short of metamorphism). 

    Scapanorhynchus ("spade-snout") is an extinct genus of shark from the Cretaceous. Often referred to as the anatomically similar goblin shark, which is distinct enough to have been placed within its own genus, Scapanorhychus had an elongated and flattened snout with awl-shaped teeth suited for tearing flesh and seizing fish. 

    S. texanus is the species that frequented the Atlantic shelf in the Late Cretaceous. The 35 mm long anterior tooth (below) is sigmoidal in shape viewed from a lateral aspect with prominent striations running from the root to the apex of the crown. It has a bulbous lingual cingulum (facing the viewer) between the furcation of the two roots, which have a prominent length. Two small, opposing cusplets are variably found on anteriors at the cemento-enamel junction (where the crown meets the root), while posterior teeth exhibit heterodontic variability, although shark teeth are generally homodontic - of the same or similar morphology.

    A 35 mm long Scapanorhynchus anterior tooth

    Some degree of difficulty can exist in identifying shark teeth from Archaeolamna kopingensis from Cretlamna appendiculata (lower left below). Likely the latter, both genera have teeth that are robust with heavy, triangular side cusps and a thick, bi-lobate root with a deep U-shaped furcation.

    Squalicorax (lower right) is a genus of an extinct Cretaceous lamniform shark related to the Great White and Goblin sharks. Its blade-like teeth possess a distinctively curved and serrated crown with a prominent notch on the mesial aspect. Its bi-lobate roots are separated by a shallow furca. Squalicorax ("crow-shark") was both a coastal predator and scavanger, as evidenced by teeth having been found embedded within the metatarsal of a hadrosaur, obviously non-marine indigenous. The species is likely S. kaupi.

    Shark teeth from Archaeolamna-Cretolamna (?) and Squalicorax

    Here are a few more examples of the many shark and fish teeth found at Big Brook. The abbreviated radicular length assists in the exfoliation of teeth under stress, which are replaced within a week by a seemingly endless supply of unerupted teeth. With the assumedly large number of sharks feeding on the shelf in the Late Cretaceous, this accounts for the large number and diversity of teeth recovered from Big Brook. Many of the bones recovered from the seafloor show fossil evidence of shark predation and scavenging and bear the distinctive teeth marks of Squalicorax's serrations. Likewise, many serrations and cusp tips of shark teeth exhibit signs of wear and chipping related to lifestyle and behavior.

    Top Row: Squalicorax, Odontaspis, Archaeolamna and Scapanorhynchus.
    Bottom Row: Two Squalicorax, Four unidentified and Enchodus.  

    On the left is one-third of a vertebral centrum of a shark with its characteristic concentric rings and saucer-like depressed center. On the right is possibly a vertebral centrum of a ray, also a chondrichthyan. 

    Vertebral centra from a shark and a ray

    Enchodus (upper right tooth above) is an extinct genus of small to medium-size bony fish in the Late Cretaceous. Thought to be a highly predatory species, it possessed fang-like teeth in the anterior, more conventional posterior teeth and a compliment of palatine teeth as well.

    First appearing in the Jurassic, belemnites are Mesozoic molluscs and members of an extinct order of the class Cephalopoda ("head-foot") that superficially appear squid-like. They possessed 10 equi-length arms studded with small inward-curving hooks used for grasping prey but lacked the pair of specialized tentacles present in modern squid. Uniquely, they possessed hard internal skeletons (below) - not hydroxylapatite of phosphatic bone - composed of calcium carbonate (calcite) in the form of a bullet-shaped rostrum or "guard." 

    Located on the posterior aspect and often mistakenly assumed to be anterior for propulsion through water, the rostrum (diagram) was attached to a chambered, conical shell called a phragmocone, and that to the tentacular head of the cephalopod. Based on the behavior of extant lifeforms, it is assumed that belemnites were powerful swimmers and active predators. 

    The rostra found at Big Brook are plentiful and easy to spot but generally fragmented. Close inspection of a rostrum in cross-section shows its internal structure to be of non-uniform, radiating concentric crystallites that are interpreted as growth rings. Early colonists suspected they formed when lighting bolts struck the ground, hence they are referred to as "thunderbolts." Locals refer to them as "bullets."

    Calcitic rostra from belemnites

    Diagram of a belemnite from

    Exogyra is an extinct genus of saltwater oyster, a common marine bivalve mollusc, that lived in great abundance within the benthic zone (just above, at and below the sediment surface) of the warm Cretaceous sea. Five species have been reported from New Jersey (C. cancellata, C. costata, C. erraticostata, C. spinifera and C. ponderosa), some of which are found at Big Brook. Exogyra and pycnodonte oysters are preserved in great numbers within the Navesink Formation's muddy glauconitic sands of Big Brook, typical of an outer shelf environment. Assemblages of the bivalves Exogyra, Pycnodonte and Agerostrea form biofacies horizons within the Navesink.  


    Another extinct Cretaceous saltwater oyster in the same family as exogyra, Pycnodonte is also a bivalve that is well represented at Big Brook. Many of the upper valves (referred to as "left") preserve the original shell coloration in the form of reddish brown radial bands, which are often discontinuous or offset indicating growth lines. The upper valve is strongly convex with concentric growth rings. Pycnodonte can reach up to 10 cm across.

    Many modern oysters fall victim to predation from crustaceans such as lobsters and crabs, and gastropods. The oyster might survive the invasive attempts by continually accreting new shell layers. Back in the Cretaceous, the predatory sponge Cliona cretacica created trace holes by boring into Pycnodonte's shell (lower left). The shell on the right is the lower (or "right") valve of Exogyra.

    Also an extinct genus of Late Cretaceous fossil oyster, this bivalve was prominent within the Navesink beds. It's semilunar shape and highly recognizable scalloped edge are characteristic. Along with Pycnodonte, it served as a biofacies assemblage horizon. 

    Inoceramus ("strong-pot") is also an extinct species of bivalve, a saltwater clam that resembles an extant oyster. It had a worldwide distribution during the Cretaceous that included the Western Interior Sea way as well as coastal regions, the Atlantic included. Its prisms of calcite confirmed it with its typical pearly luster. Inoceramus, along with the bivalves previously mentioned, are found in lag deposits that weather into the brook and provide biostratigraphic facies recognition.

    Common to the Late Cretaceous shelf's ecosystem were various arthropodal crustaceans - lobsters, crabs and shrimp - that left fragmented remains of their dorsal exoskeletal carapaces, pincers and claws. Many of the specimens may be molts rather than the remains of the parent lifeform.

    The claws of the callianassid crustacean Callianassa are often preserved within infaunal burrows and, to the astute observer, can occasionally be spotted in situ within the stream banks. Many coprolites (fecal pellets) bear a striking resemblance to exoskeletal remains in terms of glossiness, black color and similarity in shape. Exoskeletons often possess a marked symmetry, have sutures between fused segments and have surface rugosities distinctive of arthropods (bottom row, far right). 

    Top row are artifacts; bottom row are remnants of crustacean carapaces and claws.

    Typical of a coastal shelf ecosystem, many invertebrates such as worms, digging bivalves and shrimp plied the seafloor and burrowed into the shelf's sand and mud seeking food and protection from predators. Callianassa is a genus of "mud" or "ghost" shrimp common to the shelf fauna that reinforced their burrows with fecal pellets to prevent collapse. In time, the burrows filled in with sand and became iron-cemented, which is what I believe are demonstrated below. The pointed specimen at the right is a belemnite guard. 

    Trace fossils such as this - also called ichnofossils - are geological records of biological activity. They are impressions created on the surface and tunneled into the substrate of the seafloor. Ophiomorpha is a trace fossil classification or ichnotaxon of a burrowing organism in a near-shore environment. Callianassa is considered to be the best-known modern analog for this burrow. Trace fossils also include the organic digestive fecal remains or coprolites left behind by lifeforms, which are also found at Big Brook. 

    I suspect that the following specimen, displayed from three perspectives, is a cross-section of a small sand-lined burrow - a remnant of a marine organism that lived on and within the seafloor. On the left, a small circular entry on the seafloor leads to the burrow; the middle photo shows the lobate burrow from below; and on the right, the sandy substrate and burrow are visible from a lateral perspective. Other interpretations of this specimen are welcomed.

    Artifact or ichnofossil? The following specimens were extracted from Big Brook's streambed. The specimen on the left appears to contain an anastomosing network of iron-cemented burrows enveloping an oyster shell. On the right, a small section of cemented quart sand is enveloped by a similar burrow with extensive, irregular branching. Other interpretations?

    Note the morphological similarities of Ophiomorpha from the Upper Cretaceous Blackhawk Formation of Utah to the burrows found at Big Brook.

    There are many specimens or artifacts at Big Brook that defy any attempt at identification. Iron within the Navesink can cement the clayey and sandy substrate together into strangely shaped concretions. Often the result is a "fossil" that is totally inexplicable, many with curious symmetrical holes running entirely through them. Some resemble vertebral centra with small foramina, and others appear as if man made. Again, any other interpretations?

    Here's the belemnite rostrum (pictured above) that has begun to acquire a surface coating of gravelly iron-cemented material. One can envision, that once totally encrusted, it might defy identification unless visualized in cross-section.

    Unnoticed by a passing deer (and most of the visitors that come to the area), the mudflats of Big Brook are typically criss-crossed by a maze of horizontal burrows. The latter is reminiscent of the coastal shelf some 70 million years ago. 

    Note that burrowing of marine substrates was not unique to the Cretaceous. Horizontal and vertical burrowing has been going on throughout the Phanerozoic beginning in the Cambrian with the Burgess Shale type-biota. In the latest Precambrian, largely horizontal mining of benthic surfaces has been identified amongst the Ediacaran biota. It is believed that vertical subsurface excavation (whether for protection or to feed) in the Cambrian reworked the seafloor to the extent that it disrupted the cyanobacterial mat to which the Ediacara biota attached and thrived. With the coming of the "substrate" or "agronomic revolution", it is thought that might have led to their demise.  

    A heavily bioturbinated and deer-trampled mudflat alongside Big Brook

    Most assuredly, there's a lot to experience and comprehend in the "piddly little dribble" of Big Brook.

    Bedrock Geologic Map of Central and Southern New Jersey by James P. Owens et al, 1998.
    Bedrock Geologic Map of of the Freehold and Marlboro Quadrangles, Middlesex and Monmouth Counties, New Jersey by Peter J. Sugarman and James P. Owens, 1996.
    • Big and Ramanessin Brooks by the New York Paleontological Society, Field Trip 2002. 
    Callainassid, Burrowing Bivalve, and Gryphaeid Oyster Biofacies in the Upper Cretaceous Navesink Formation, Central New Jersey: Paleoecological Implications and Sedimentological Implications by J.B. Bennington et al, Department of Biology, Hofstra University.
    • Cretaceous Fossils of New Jersey - Part I by Horace G. Richards et al, 1958.
    Cretaceous Stratigraphy of the Atlantic Coastal Plain, Atlantic Highlands of New Jersey by Richard L. Ollson, Department of Geological Sciences, Rutgers University, GSA Centenial Field Guide-Northeastern Section, 1987.
    Geology Map of New Jersey, Department of Environmental Protection, Geological Survey, 1999.
    • Greensand and Greensand Soils of New Jersey: A Review by J.C.F. Tedrow, 2002.
    • New York Paleontological Society. Established in 1970, individual and family memberships are open to all, regardless of education or previous experience, It's a fantastic way to visit Big Brook and many other fossil-collecting localities in the Northeast with an enthusiastic and well-informed group of amateurs and professionals. Meetings are held in the American Museum of Natural History in New York City and includes an outstanding newsletter. Visit them here to join. Yes, I am a member.
    • Paleocommunities and Depositional Environments of the Upper Cretaceous Navesink Formation by J. Bret Bennington et al, Department of Geology, Hofstra University, 1999.
    • Paleontology and Sequence Stratigraphy of the Upper Cretaceous Navesink Formation, New Jersey by J. Bret Bennington, Hofstra University, Long Island Geologists Field Trip, 2003.
    Pictorial Guide to Fossils by Gerard R. Case, 1992.
    Roadside Geology of New Jersey by David P. Garper, Mountain Press Publishing Company, 2013.
    Shell Color and Predation in the Cretaceous Oyster Pycnodonte Convexa from New Jersey by J. Bret Bennington. Hofstra University.
    Summary of Lithostratigraphy and Biostratigraphy of the Atlantic Coastal Plain by Richard K. Ollson, Rutgers University.
    Uppermost Campanian-Maestrichian Strontium Isotopic, Biostratigraphic and Sequence Stratigraphic Framework of the New Jersey Coastal Plain by Peter J. Sugarman et al, GSA Bulletin, 1995.

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    Mushrooms and toadstools. Mold and mildew. Puffballs and earthballs. Jellies and slime. Rusts and smuts. Stinkhorns and bloodfoots. The only thing more colorful than their names is their staggering diversity and bizarre biologies. This post is a continuation of the mycological mission I initiated in Part I (here), in which I discussed the lifecycle of the mushroom. In this final fungi post, I document some of the more remarkable specimens sprouting in my yard and down the street.
    Amanita muscaria var. guessowii
    “Esteemed by both maggots and mystics” (David Arora), this hemispherical-shaped, yellow-capped, conifer-loving beauty is known as the American Eastern Yellow Fly Agaric. The “fly” designation, according to one source, refers to its use in Eastern Europe as an insecticide, supposedly lethal to flies when mixed with milk.

    The warts on the cap’s surface are remnants of the “universal veil”
    that shrouded the juvenile mushroom as it germinated through the soil.

    Amanita is a study in contradictions. While some are wildly hallucinogenic and delicious beyond compare, a few are the most toxic of all mushrooms with names such Death Cap and Destroying Angel. After the ingestion of a toxic Amanita, it can take a few days for symptoms to appear, which is particularly dangerous since its toxins insidiously demolish one’s kidneys and liver.

    In his memoires, Voltaire recounted Holy Roman Emperor Charles VI’s death from eating sautéed amanita as, “The dish of mushrooms that changed the destiny of Europe.” Because amanita resembles several other edible species, fungiphile and author Arora warns, “When in doubt, throw it out.”

    Of the 16,000 species of mushrooms identified by mycologists, the red and white-spotted fly agaric
    is the iconic mushroom. It's often referred to as a toadstool due to its poisonous and psychoactive properties.

    Omphalotus illudens
    Like an annual time clock during the second week of August, dense clusters of bright orange mushrooms appear at the foot of an aging oak down the street. With the same regularity, my neighbor frustratingly digs up the crop in hopes of eradicating it, only to see it return the following year. Picking apples in an attempt to eradicate the tree is futile. As long as the "rooted" mycelium remains viable within the soil, the fungus will continue to spawn new mushrooms.

    Mushrooms are fruiting through a crack in the sidewalk where the tree’s roots have barely broken the surface.

    Omphalotus is also known as the Jack O’Lantern mushroom likely due to its pumpkin-color, although some sources attribute the name to its eerie property of neon-green bioluminescence. About 90 species of fungi glow in the dark along with certain bacteria, algae, marine creatures and insects such as the familiar firefly. Anyone can observe it in a forest on a dark summer’s night, although I’ve failed to photograph the phenomenon in my dark basement three years running.


    Some references state that bioluminosity occurs at all stages of the fungi’s lifecycle, while others indicate that it only occurs in fresh specimens in which spores are still forming, so timing is critical. Light-emission is the result of oxidation involving an enzyme called luciferase. One theory is that insects receptive to the emissions are attracted to the luminescence, which assists in spore dispersal.

    The mushroom caps start out flat but become centrally depressed, eventually becoming wavy and lobed.

    Omphalotus is frequently mistaken for its lookalike, the prized chanterelle mushroom Cantharellus, a $1.5 billion global market, hence its occasional reference as False Chanterelle. The similarity is potentially hazardous, since chanterelles are highly edible and our Jack O’Lantern is deadly poisonous. Muscarine, its neurotoxin, produces GI symptoms, visual disturbances, irregular pulse and respiratory failure.

    In Polish, there’s a phrase, "A sapper (field soldier) and a mushroom collector make a mistake only once." In spite of its toxicity, Irofulven, a chemically modified version of the mushroom’s toxin, is currently undergoing clinical trials as an anti-tumor agent.

    Coprinus plicata
    With a delicate, pleated cap, many of the Coprinus mushrooms are extremely ephemeral, often lasting only a few hours in the morning. The reason is that its gills autolyse (self-digest) and deliquesce (turn to liquid) at maturity into a black, inky fluid that drips to the ground, hence their common name of Inky Caps. Autodigestion is a unique method of spore dispersal. As the spores at the mushroom’s periphery ripen first, the release of enzymes causes the cap to curl back spreading the gills and discharging the spores into the air. What’s left is a ragged stalk.

    The autodigestive-spore releasing process is recalled in Shelley’s memorable lines of The Sensitive Plant:

    “Their mass rotted off them, flake by flake
    Till the thick stalk stuck like a murderer’s stake;
    Where rags of loose flesh yet tremble on high,
    Infecting the winds that wander by.”

    Ionotus tomentosus
    This leathery bracket fungus is primarily a pathogen of spruce forests but also infects other evergreens. It was fruiting in my back yard at the base of a tall, old spruce. It’s frequently associated with infections of tree roots and their mortality. Last year, I cut down two nearby spruces and wonder if this one will be next. The fungus is often associated with spruce beetles.

    It’s a member of phylum Basidiomycota (see post Part I here), but rather than gills, its spores are produced within tiny, circular tubes that line the undersurface of the fruitbody. That gives the surface a perforated appearance, hence the fungi’s alternate name of polypore.  

    Ganoderma applanatum 
    In New England, it’s very common to find massive, slow-growing, beeches on the grounds of stately old homes, churches and cemeteries, planted for their dense shade and botanical grandeur. For years, this thin-barked beech up the street began to host an array of huge bracket fungi on its south-facing side. Passersby couldn’t resist stopping for a look. I took the presence of the fungi as an indication of ill health. Sadly, this summer the majestic tree suddenly became leafless and was cut down. It left a huge void both on the ground and amongst the canopy of the surrounding trees.

    Appearing somewhat near the base of the tree, the polypore is gray to brown in color, and often green with algae. They are also called Artists’ Conks since lasting pictures can be carved onto their undersurface. When they fruit on live trees, they are often parasitic and allow insects and woodpeckers to invade the bark.

    Its layers are an indication of its age. A large specimen can liberate up to 30 billion spores a day for 6 months of the year. Multiply that by its age of about 10 years for the polypore seen below! High spore production illustrates the mathematics of survival, since most spores fall upon a nutritionless, hostile substrate.

    Fomitopsis pinicola
    Like Ganoderma, this Red-Banded polypore is a common, perennial bracket fungus that was boldly attached to another spruce in my back yard. Its concentrically grooved bands of yellow to orange and red, its thick pizza crust margin, and its resin-coated surface make it both hard to miss and misidentify. Its preference is dead wood (conifers in particular), rotting logs and stumps rather than live trees.

    Scleroderma citrinum
    This Earthball, along with related puffballs, earthstars, bird’s nest fungi and stinkhorns, produces its spores inside the fruitbody rather than on the undersurface of mushrooms. At maturity, the fruitbody ruptures, such as during a rain, exposing a purple-brown spore-mass, freeing the spores to inoculate the wind. Unlike puffballs that develop an aperture through which the spores escape, earthballs break up to release their bounty.

    This spherical yellow-brown Earthball with its ornately decorated, raised mosaic pattern was fruiting in the woods in my neighborhood. They’re all classified as Gasteromycetes or “stomach fungi.”

    Fusicolla merismoides (possibly)
    Also in the woods, this amoeba-like slime mold appeared after a soaking summer rain. The gelatinous oozing, vomitous blob looked like something out of a B-movie. Slime molds (mould is the British version) produce spores and thus were formerly classified as Fungi, but many taxonomists consider them as protists (see post Part I for a taxonomic explanation here). Since mycologists traditionally group and discuss them with fungi, so have I, especially since they appeared along with the mushrooms this summer.

    Typically found on soil, lawns, mulch and on the forest floor where shady and damp, they can travel several feet and climb any object to feed on microorganisms that live on dead plant material such as bacteria and fungi, and contribute to its decomposition. The slime searches for a host, surrounds it, and then secretes enzymes to digest it. Protoplasm at the cell’s periphery creates a type of movement called “shuttle streaming.”

    Slime molds, while brainless, are smarter than they look. Amazingly, some are capable of navigating and solving an agar maze in search of food. This display of “intelligence” occurs by anticipating thermal changes at predictable time intervals. When it’s time to fruit they even migrate to a more desirable site for spore dispersal, often quickly at night to minimize the risk of dehydration. Despite being a single cell, each part of the plasmodium reacts to environmental information independently. By combining the reactions, the mass responds without even a conscious thought. “Nothing can stop it!”


    Fuligo septica
    The yellowish, bile-colored Dog Vomit (or Scrambled Egg) slime mold was believed to be used by witches to spoil their neighbors’ milk. I found this specimen hiding under a rotting log in a nearby woods. Like the slime above, the amoeboid mass migrates in search of nutrients. Under adverse conditions such as dryness or cold temperatures, the slime can form a hardened, resistant structure called a sclerotium, which is capable of reforming and reinitiating its protoplasmic exploitations.

    Its yellow pigment, fuligorubin A, chelates metals and converts then into inactive forms, which accounts for the slimes high resistance to toxic levels of metals (up to 20,000 ppm). The pigment is also thought to be involved in photoreception for purposes of energy. Not that you’re tempted, but it’s inedible.

    Genus Ramaria (possibly)
    Another member of phylum Basidiomycota, coral fungi come in many colors, and many are tasty. The fruitbody is densely branched and fruits on the ground in woods. Although related to mushrooms and not the marine animal for which they resemble, corals bear no anatomical likeness to mushrooms. But like the undersurface of mushrooms’ caps, their many branches provide a high surface area for the basidia, the spore-producing structure of the fungus, similar to mushroom’s gills, pores, teeth and folds (see Part I).

    There are many forms of coral fungi, originally lumped into one unwieldy genus. Now there are over 30 genera, looking coral-like due to convergent evolution.

    My “Neighborhood Fungus Watch” wouldn’t be complete without mention of the ubiquitous gray-green rosettes on trees, tangled masses of hair suspended from branches, miniature goblets on the ground and yellow-orange crusts on rocks. Lichens are neither plants nor single organisms but are “miniature ecosystems” (Hinds). 

    They are a partnership of two, and sometimes three, lifeforms that coexist as one for their mutual benefit. It’s a symbiotic association between a species of fungus (the mycobiont) and a species of photosynthetic algae (a photobiont, usually Trebouxia).

    The algal component is either eukaryotic green algae or prokaryotic blue-green algae (explained in Part I). With over 14,000 species to date, lichens are classified within Kingdom Fungi based on the Latin name of the fungal partner (which is usually an Ascomycota or “cup” fungi), since the relationship is largely fungal (90%). Therefore, lichens are often referred to as “lichenized” fungi. Most of the vegetative body of the lichen, called the thallus, is formed by the fungus.

    The algal component lives not within the actual cells of the fungus but sandwiched within the body of the fungus (the medulla) between the upper and lower fungal cortex. Anastomosing hyphae form a loosely arranged network that are in communication with the algal cells. Strands of root-like hyphae (rhizines) attach the lichen to the substrate.

    Schematic cross section through the thallus (body) of a flat, leaf-like (foliose) lichen.

    The algal member provides energy to the fungus in the form of manufactured simple carbs such as glucose or sorbitol. In return, the alga gets a happy home with a favorable microenvironment from desiccation, protection from excessive UV radiation and mineral nutrients from the attachment-substrate and the atmosphere. Most vascular plants would be incapable of populating the lichen’s exposed, inhospitable, nutrient-poor habitats.

    Therein lies the enigma of lichens! They are the hardiest of “plants” capable of surviving arctic cold, desert heat and extreme drought. In a 2005 test, lichens even survived 15 days of exposure to the vacuum of space on a Russian rocket. Yet, they are incredibly sensitive to pollution since they absorb water and nutrients from the air. Devoid of lichens, industrial regions of the world are referred to as “lichen deserts.” In my nearby Boston, you don’t start seeing lichen-covered rock walls until several miles from the city until reaching the “clean air” of the suburbs. Thus, lichens are bio-indicators of air quality. There's even a profound association between lichen presence and a reduced risk of lung cancer. Another reason to look down at the ground!

    Lichens are divided into groups or growth forms based on modes of substrate attachment. The three most common are: crustose (crust-like), foliose (leaf-like) and fruticose (long and hairy often with cups).

    Evernia prunastri is an antler-like fruticose (hairy), “oakmoss” lichen that favors growth on decaying oak.
    They are commercially harvested in Europe and sent to France for their fragrant compounds used in perfumes.
    Typically growing on bare, exposed rock especially at high elevations, this mosaic of Rhizocarpon geographicum is a crustose (crust-like) “map” lichen that is tightly adherent to the rock substrate and even within the substrate. Several species of crustose lichens often occur together on the same substrate. Lichenometry is used by climatologists to date rockslides and glacial deposits such as moraine systems based upon their slow growth rate. 
    Flavoparmelia caperata is a foliose (leaf-like), “common greenshield” lichen on a tree. Powdered forms have been used to treat burns in Mexico. Native Americans have used similar forms for dyes. The basic pattern of growth for lichens is to expand centripetally from the point of origination. This gives the thallus a rounded appearance and allows an estimation of the rate of its growth. Like rocks that exhibit appreciable differences in their physical and chemical properties, the barks of trees have varying textures, moisture-carrying capacities and chemistires such as pH. Thus, lichens show specificities as to their preferential substrates.

     Amazing lichen facts that your friends probably don’t know:
    1.) Lichen symbiosis may have been one of the first steps in the colonization of land. In the Precambrian, lichens may have lowered CO2 levels sufficiently to plunge the Earth into global glaciation typified by Snowball Earth between 750-580 Mya. Their eventual terrestrial colonization may have raised the atmospheric O2 levels enough to permit the Cambrian Explosion.
    2.) Lichens can physically weather a granite substrate by penetrating intergranular surface boundaries, voids and cleavage planes. The swelling and contraction of hyphae can then break up the rock. They can chemically weather granite by leaching out potassium and iron. On calcareous (limestone) rocks, lichens produce weak acids that dissolve the substrate.
    3.) Beatrix Potter, the celebrated author of Peter Rabbit fame, was a pioneering mycologist who studied and experimented with fungus germination under the microscope as early as 1887. She published Les Champignons on fungus and lichens with over 65 original, watercolor drawings. Her scientific fungal paper was read by a male colleague before the men-only Linnaean Society of London, but it was rejected from publication because of her gender. Fortunately for children everywhere, her artistic talents found creativity elsewhere.
    4.)  Fungi and algae, although capable of forming an intimate partnership, are totally unrelated phylogenetically. Fungi and humans share a common ancestor and are more closely related. One would expect that all lichens are more closely related than they would be to other fungi. Instead, the lichen partnership has evolved a myriad of times, because the DNA and genes of different lichen species are more closely related to non-lichen fungi than they are to other lichen. (Gargas et al, Multiple origins of lichen symbiosis in fungi suggested by SSU rDNA phylogeny. Science 268: 1492-1495, 1995).

    Nudgers and shovers
    In spite of ourselves.
    Our kind multiplies:
    We shall by morning
    Inherit the earth.
    Our foot’s in the door.
    Mushrooms in The Collected Poems by S. Plath, 1959

    With great appreciation, I thank professional mycologist Taylor Lockwood and amateur “mushroom expert” Michael Kuo for their expertise in identifying many of the more obscure mushrooms in my neighborhood. Their respective links are below.

    Kingdom Fungi by Steven L. Stephenson
    Macrolichens of New England by James W. and Patricia L. Hinds
    Mushroom by Nicholas P. Money
    Mushrooms Demystified by David Arora
    Mushrooms of Northeast North America by George Barron
    Mushrooms, Simon and Schuster’s Guide by Gary H. Lincoff

    Tom Volk here

    Michael Kuo here
    Michael Wood here
    Taylor Lockwood here
    North American Mycological Association here

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    Virtually every geology-based road trip I've been on has had its share of unforgettable side trips, off beat detours and unplanned turn offs. The best part, second to the geology, was the adventure of the unexpected and the inexplicable waiting at every turn.

    That’s when you see the unusual signage, the eccentric pieces of art, the unique architecture, the kitschy sculptures, the cheesy tourist stops, the poignant juxtapositions, and all the wacky, tacky, bizarre and oddball attractions that are so characteristic of Roadside America. It’s also when you find remnants of vanishing America - the diners, drive-ins, juke-joints and storefronts that have been thoughtfully preserved or recklessly abandoned to the ravages of time. 

    Here's what I stumbled on this November while traveling with my friend and geologist  Wayne Ranney on the roads and backroads between Phoenix, Arizona and the Mexican border. This is my third post in this series in what has become a tradition following our geological excursions. The other two may be found in the "Index to Topics" in the column to the right under "Roadside America."

    Outside Clifton, Arizona (2012 population of 3,447), its drive-in theatre has become pastureland. Along with nearby Morenci, the region rose to prominence subsequent to the discovery of copper in 1872. Drive-ins were an innovation of the 1950’s. An icon of American civilization, they were a perfect marriage of Hollywood and the automobile. Once a mainstay of every American city and many rural towns, the country had over 4,000 during the 60’s. They provided the family with a night out together, and for teenagers, you know what else. In the 70's and 80's, the industry gradually succumbed to competition from cable, movie rentals, digital media and land development. As of this writing, Arizona still has two with 357 still clinging to life nationally, spurned by a “Save the Drive-In" movement.

    On the foothills of the Superstition Mountains (home of the Lost Dutchman's Gold Mine), for a small town such as Apache Junction in south-central Arizona on Route 88, signage was an essential component in getting a car to pull over in the 50’s and 60’s. Kovac's Corner was a beer and chicken joint that burned down years ago. They broasted chicken using a pressure fryer. The Broaster Company of Beloit, Wisconsin licensed their trademark to over 5,510 purchasers of their equipment that followed their cooking specifications, recipes and certification process. Sounds like the beginning of fast food to me!

    Literally across the street, beer and chicken headline a newer version of the menu today. Nothing gets my digestive juices flowing more than an enormous chicken alongside my table.

    This turn of the century, headboard-fence in Bisbee, Arizona caught my eye. In 1880, Bisbee was founded as a copper, gold and silver mining town, named after Judge DeWitt Bisbee who financially backed the adjacent Copper Queen Mine. Mining in the Mule Mountains was incredibly successful back in the early 1900's with Bisbee soaring in growth AND culture. In 1917, the open pit mine fulfilled the heavy copper demands of World War I, but in 1975 the Phelps Dodge Corporation halted its Bisbee mining operations. The resulting mass exodus of workers might have been the end of the town, but mine tours and tourism revived the local economy. Today, "Old" Bisbee, the town above the Lavender Pit Mine, has gone from "Copper to Culture." It's totally reborn as a haven for artists, hippies and everyone wanting fresh mountain air, gentrification in a renovated period bungalow, the local cuisine or a romantic night in an antique-filled hotel.

    I did a double-take at this New Age front on an old building-cum-home in Bisbee. One can only imagine the sheek decor inside. During its mining heyday, Bisbee produced nearly 25% of the world's copper and was the largest city in the Southwest between Saint Louis and San Francisco.

    This "masthead" decorates one corner of the building.

    This demising wall across the street was intensely muralled. Notice the graffiti proclaiming "Old Bisbee."

    And this creative gallery sign was next door. The "Five C's" of Arizona's economy are: Cattle, Copper, Citrus, Cotton and Climate. Bisbee deserves a sixth "C" for Creative.

    Here's a 60's mega food-sculpture in newer Bisbee, down in the flats below the Lavender Pit mine.
    Bisbee is the nation's southernmost mile-high city.
    Prior to 1906, Tortilla Flat in south-central Arizona was a stagecoach stopover on the Yavapai Trail between Tonto Basin and the Salt River Valley. Later, as the Apache Trail, it became a freight road for the construction of the 1911 Roosevelt Dam on the Salt River that flows through Phoenix. The flat became an important supply stop on the road. Today, the trail is officially Arizona Highway 88, while Tortilla Flat lures travelers for lunch and ice cream. Within its handful of stores, over 100,000 single dollar bills are plastered over the walls, rafters and ceilings of every room, including the rest rooms. The name "Tortilla Flat" supposedly originated from the cowboys who drove cattle from Globe to Phoenix, who camped at the flat having forgotten to pack flour to make their tortillas. An alternative explanation offers the rock strata stacked like tortillas.

    Believe me now?

    Arizonans are an independent and courageous lot. Apparently, this individual took the "No Smoking!" warning at the pumps as merely a suggestion rather than a really good idea. "It's never gone off yet!" Note "Safety Award" on the right sleeve. Needless to say, we departed rather quickly. Location shall remain unmentioned.
    Mobil was previously known as the Socony-Vacuum Oil Company back in the 1930's. Socony stood for Standard Oil Company of New York. It was an American oil company which merged with Exxon in 1999 to form ExxonMobil. Today, Mobil continues as a major brand name within the combined company, as well as still being a gas station. This weather beaten sign hangs above Arizona Highway 60 in the center of Miami, Arizona. Miami is a another classic Western copper boomtown, though its copper mines are largely dormant now. In an incipient revival akin to Bisbee's, the old downtown has been partly renovated, and low-cost housing is attracting new residents with an artsy and antique flare. It's only a matter of time.
    Also in Miami is a vestige of another vanishing tradition, the "Blue Plate Special." Originally served on a blue plate with partitions for a meat and three vegetables, a low priced meal was served by diners and cafes back in the 20's through the 50's. It was a good deal but "No Substitutions." A Blue Plate Special has become a colloquial expression for an inexpensive full meal but also connotes any good deal with "all the fixins." This sign on an abandoned diner has received a new coat of paint. Maybe Miami's revival will reopen the kitchen.
    In Miami, a preservationist-minded individual is holding on to the past. On Live Oak Street (U.S. 80), this Art Deco style gas station was literally a museum both inside and out - old cars, vending machines, tools, signs. Notice the building's white, tiled facade, period glass bricks and rounded corners.
    When was the last time you saw a gas pump that looked like this? That's glass not plastic!
    Unbeknownst to the casual observer driving through town and not even a half mile from the main street resides the massive Miami Copper Mine. Along with the mining town of Globe seven miles to the east, they lie in the foothills of the Pinal Mountains within the Arizona Silver Belt dating back to the 1870's. In the 1880's, the price of silver fell, while copper rose exponentially. The porphyry copper deposits were in bodies of ore that were disseminated through the rock mass rather than in concentrated veins and pockets, hence the development of the massive pit mine.
    In far southern Arizona, this sign was a first for me. Any guesses precisely where we are?
    Here's a hint.
    We're in Naco, Arizona, at the Border Fence or Wall between Mexico and the United States. 96.6% of apprehensions along the 1,951-mile border between the two countries occurs along the country's southwest boundary and traverses a variety of terrains including urban areas and deserts. The barrier strategically exists where illegal crossings and drug trafficking have existed in the past. In addition to the physical barrier, a "virtual fence" of motion sensors and video cameras watches everything and everyone that moves. Note three of them on tall poles down the road. We counted over two dozen white Border Patrol vehicles on maneuvers in one hour. Critics in Arizona and Texas assert that the fence adversely isolates endangered species in critical migration corridors and jeopardizes fragile ecosystems much the way roads and canals have compartmentalized the Florida Everglades (recent post here). In 2010, a Rasmussens Reports survey indicated that 68% of Americans are in favor of the U.S.-Mexico Border Fence.
    Where would Clark Kent have gone nowadays to make a quick change into Superman? Probably Starbucks. Statistics-websites state that there are currently only four outdoor telephone booths left in New York City. Thinking for a minute, I wouldn't know where to find one in my home town. The once-ubiquitous "street closet" is becoming increasingly difficult to find for obvious reasons, and towns nationally are requesting that they be removed as an unkempt, albeit stench-filled eyesore. Recently, Verizon announced that it would start providing wireless computer connectivity in the vicinity of its previous phone booths in Manhattan. Think about that for a moment. On an ironic note, no one heard your private conversations if you made them from a public phone booth, but virtually everyone within earshot hears everything you say on a wireless phone. This one in the rural hamlet of Portal, in southeastern Arizona, has been stripped of its essential item - the phone. At least the booth is still there for Clark! Geologically, Portal is at the mouth of a canyon referred to as the Yosemite of Arizona. The region is also a mecca for birders.
    This store or perhaps a gas station with its setback from the road still retains its old West facade. We're near the mini-hamlet (year 2000 population of 309) of Elgin. It's the first location in Arizona to engage in commercial winemaking, which we experienced first hand.
    Right next door was an antique railroad car gradually decomposing into the landscape.
    You never know what you're gonna find.
    Back in Tucson, after a 1,300-mile geological road trip and mystery tour, we got an early start to investigate the metamorphic core complexes that encompass the valley. I did a double take at this raptorian red light.
    Thanks again, Wayne.

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    In the Tucson Mountains west of Tucson, Arizona, lies the unsuspecting rocky outcrop of Signal Hill. Just a short hike from the scenic Bajada Loop Drive through the Sonoran Desert in Saguaro National Park West brings you to the hillock’s rubble-covered crest of sun-baked boulders where a millennium-old gallery of petroglyphs (Greek for "stone-carvings") is on display.

    Members of the pre-Columbian Hohokam (HO-HO-kam) created the rock renderings with a stone and hammerstone. By chipping, incising and abrading through a micro-thin, dark coating of desert varnish into the lighter, underlying rock, they fashioned images commonly called rock art. Leaving no written history, the images afford us an opportunity to look into the past and gain insight into the Hohokam's lives and thoughts. 

    This High Dynamic Range photograph centers on a one-foot diameter Hohokam spiral geometric.

    The Hohokam people thrived in central and southern Arizona from about 400 to 1450 AD. They were farmers, hunters and gatherers, who built over 1,000 miles of elaborate canals in the Phoenix area and cultivated crops of corn, cotton, squash and beans. In the region of Signal Hill, they occupied the river valleys and deserts between the Tucson Mountains and the Rincons.


    After thriving in the Sonoran Desert for over 1,000 years, Hohokam society began to decline and collapse over the course of several generations. During the Protohistoric Period, between the Hohokam occupation and Spanish contact, the area appears to have been occupied by Sobiapuri (Upper Pimam) and Tohono O'odham people. 

    When Spanish explorers arrived in the 1500's, they found Hohokam villages in ruins. Their fate is both controversial and mysterious, whether related to droughts, soil depletion, warfare, disease or internal strife. Archaeologists that search for clues also look for direct links to indigenous Native Americans like the O’odham Nation that practice Hohokam’s desert traditions such as the annual saguaro cactus fruit harvest. 

    The Hohokam’s petroglyphs at Signal Hill are reminiscent of life forms such as snakes, lizards, bighorn sheep, dogs, plants and stick-figure humans, but the majority are abstract geometrics of circles, spirals and lines. Their meaning remains unknown, whether pre-historic graffiti, artistic, symbolic conveyance of a message to passersby or their descendants, astronomical, religious or ceremonial. Perhaps their significance lies in the very act of creating the images rather than the message they convey.

    Petroglyphs litter the crest of Signal Hill seen from the trail

    Found throughout the Southwest, and in fact worldwide, desert varnish is the canvas on which many Native American cultures engraved their rock art. Pictographs are often confused with petroglyphs, which are literally drawn or painted on rock faces with naturally-occurring pigments made from clays and minerals. Pictographs are not as durable as petroglyphs unless located in protected settings such as rock shelters or caves. 

    Desert varnish is typically found on resistant rock surfaces that are subjected to periodic wetting and drying in arid regions of the world. "Rock" varnish is a more appropriate term, since it also occurs in tropical, arctic and alpine environments. Its coating ends with an abrupt boundary on rocky substrates. The sharp demarcation is suggestive that it is derived from external sources. A long standing debate exists as to whether the varnish's formation is microbially-mediated, deposited by inorganic processes or more likely a combination of biological, physical and chemical processes.

    Micro-fungi have been cultured from the varnish, but it remains unclear whether fungi or bacteria precipitate the varnish or if microbial components complex with metals in the varnish-forming process. It has been theorized that the varnish’s thin patina protects underlying microbes from exposure to desiccation and UV radiation. The following schematics summarize three popular models for the formation of desert varnish.

    Three schematic models of varnish formation showing: evaporative leaching of the underlying rock substrate followed by re-precipitation (a process whereby varnish develops from the inside out); diagenesis of detrital dust particles after accretion to the substrate; and direct chemical precipitation of dissolved atmospheric trace-metal components in rain water, fog droplets and aerosols (a model which explains varnish's conspicuous association with moist surfaces which favor microbial colonization). HFSE's are high field strength elements: Zr, Nb, Hf and Ta. REE are rare-earth elements. See author's article for detailed explanation.
    Modified from Thiagarajan and Lee (2004)

    Numerous chemical elements are found in varnish but predominantly clays and oxides of manganese and iron, making it appear black and reddish-brown, and at far greater levels than the neighboring substrate and soils. Mixtures of oxides are responsible for intermediate shades of brown. The varnish is almost as hard as quartz and yet extremely thin, commonly a hundredth of a millimeter in thickness (<200 µm). 

    It takes thousands to tens of thousands of years to coat a rock with varnish in the arid conditions of the Southwest with growth rates from <1 to 40 µm per thousand years. That qualifies desert varnish as the slowest forming terrestrial sedimentary deposit! Varnish's structure appears micro-laminated in microscopic cross-section, reminiscent of a stromatolite's onion-layered macro-stratification. 

    Attempts to utilize varnish for paleo-dating have proven unreliable; however, its usage as a paleo-climate indicator does shows promise. Incidentally, varnish may have planetary analogues, Mars in particular, which has fueled speculation of its potential usefulness in the search for life on other planets. 

    The bedrock rock type in the immediate region of Signal Hill is granodiorite, a coarse-grained, intrusive igneous rock intermediate in composition between granite and diorite. These rocks were generated within a volcanic caldera, a collapsed magma chamber, at the end of the Cretaceous from a subduction zone (Sevier-Laramide compression) at the continent’s western margin, a time when at least seven volcanoes were active in southeastern Arizona.

    Long after the cessation of volcanic activity and related to continued plate subduction with an altered geometry around 30-35 million years ago, extension (pulling-apart) and heat from within the Earth's crust separated the landscape into linear ranges with intervening basins. Portions of the extinct caldera were faulted upward into a range, the Tucson Mountains, while other portions dropped into the nearby basin and were covered by basin fill sediment.

    Bedrock map showing relationship of "upper plate" Tucson Mountains and "lower plate" Catalinas with the Tucson Valley basin intervening. Note the location of the Catalina detachment fault.
    Modified from Arizona Geological Survey's Open File Report OFR 06-01

    Brittle, faulted-blocks of the Tucson Mountains represent an unmetamorphosed “upper plate” (not to be confused with a tectonic plate) of an arched "metamorphic core complex." Complexes are enigmatic, controversial and only recently described geologic features of Arizona’s Basin and Range province.  The Tucson-upper plate slid off (detached) from the “lower plate” along an intervening, near-horizontal “detachment fault”, which bowed upward into a blister-like uplift.

    Uplift occurs in response to tectonic denudation (i.e. erosion) and the inflow of hot, middle crust. Portions of the lower plate are exposed by erosion and others lay buried within the Tucson basin (called a graben, German for grave). The metamorphic core of the “lower plate”, stretched and deformed plastically rather than brittlely, forms the Santa Catalina Mountains across the basin. These domal uplifts are not confined to the Basin and Range of Arizona but follow a sinuous belt from southern Canada to northwestern Mexico. 

    Schematic formation of the Tucson-Santa Catalina metamorphic core complex.
    Note that the west to east perspective in the diagram is opposite that of the bedrock map.
    A, Tucson Mountain volcanics and domal uplift; B, Volcanism and detachment of upper plate from lower plate; C, Basin and range faulting with downdropping of Tucson graben; D, Basin sediment fill.  

    The ruggedness and colors, the distinctive look and feel, the topography and climate, and the rocks exposed in Saguaro National Park West are a compendium of the state’s billion year-plus geologic history. On our return hike from Signal Hill, the setting sun and rising moon, the billowy clouds and blue sky, the saguaro and prickly pear, and the spirits of the Hohokam were in exquisite balance.  Please enjoy the following photos as our day gloriously gave way to night.


    High Dynamic Range digital photograph

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    Every blogger knows the challenge. What shall I blog about next? What photos should I use? By the time the end of the year rolls around, there are always a few posts that never quite made it. And so, with this final post of the year, here they are from here and there. Please visit the same for 2012 here.

    Flying High Above Boston’s West African Harbor Islands

    Looking frigid and uninviting in mid-winter, Boston’s Harbor Islands are best explored during the summer months. The harbor is sprinkled with 38 of them, most designated as National Recreation Areas. Many have fascinating histories such as Georges Island (apostrophes are not used) with Civil War-era Fort Warren used as a Confederate prison and its resident ghost, the Lady in Black. Little Brewster is home to Boston Light, the oldest continually used lighthouse in the U.S. from 1716. Worlds End has plantings and roads by legendary 19th century landscape architect Frederick Law Olmsted, the designer of Central Park in NYC and Boston's Emerald Necklace park system. There’s even an abandoned, off-limits Nike missile silo on Long Island.
    As for the region’s geology, Boston Harbor is a glaciated structural basin that has been inundated and modified by post-glacial sea level rise in the last 15,000 years. It contains dozens of exposed and submerged Pleistocene-age drumlins and other glacial features modified by coastal processes. The bedrock crops out at numerous locations and consists of the Late Proterozoic Boston Bay Group, rocks of the Avalonia terrane that accreted to Laurentia during the Middle Paleozoic.
    The group consists of fine-grained clastics of the Cambridge Formation (“Argillite”) and coarse-grained clastics of the Roxbury Conglomerate better known as “puddingstone”, the Commonwealth’s state rock. The terrane of Avalonia rifted from its peri-Gondwanan, Southern Hemisphere-berth off the northern edge of the West Africa craton (although some advocate a northern South America provinence). It then drifted some 6,000 miles during the Ordovician across the Iapetus sea to its present location in Boston Harbor, accreting (attaching) in the process to a large portion of the Appalachian orogen along Laurentia’s northeast coast. 

    On an Appalachian-Derived Beach at Fort Lauderdale

    This Fort Lauderdale beach scene is far more welcoming meteorologically this time of year. It depicts a commonplace entity with the warming climate – beach erosion and restoration. Sediment (mostly sand) is typically lost through longshore drift (movement of material by waves that approach at an angle to the shore but recede directly away from it) and from changing ocean currents and storms. A wider beach reduces damage to coastal structures by dissipating energy across the surf zone. It also protects upland structures and infrastructure from storm surges, tsunamis (not on this passive marginal coast) and unusually high tides.
    Of course, Floridians will need to deal with the issue that everyone must confront, rising sea levels from melting glacial ice. It won’t be the first time it has risen. Fluctuating glacial periods of the Pleistocene triggered vacillating high seas that periodically flooded coastal plains. Before that, during the Cretaceous, North America’s central continental and coastal lowlands were completely submerged by global high seas of the Tejas transgression.
    By the way, Lauderdale’s beaches are composed of brownish, quartz sand not whitish, calcium carbonate, which is not what one would expect considering Florida’s carbonate-platform heritage. Silicon dioxide-rich sand was transported downbeach from the eroding Appalachians Georgia-way by longshore currents during the Cenozoic. Next time you stroll along the beach further south, check out a handful of sand. It gets whiter as its carbonate content increases with distance from its granitic source up north.

    Living Cretaceous Fossils in Bloom in Boston’s Backbay

    The annual explosion of pink and white magnolias in bloom is one of Boston’s first rites of spring. The city's floriferous trees have more to offer than large flowers, showy colors and fragrant scents. There's a tale of evolution to be told here.
    You see, beetles pollinate magnolias, not bees as one might expect. Bees were not around in the mid-Cretaceous (about 100 million years ago), when magnolias were evolving. That pollinator relationship has changed little over the millennia since the co-evolution (mutual evolutionary influence) of insects and angiosperms (flowering plants). Magnolia flowers don't produce nectar, the sugary secretion that encourages insect visitation (and hence pollination). They do produce large quantities of pollen that's high in protein, which beetles use for food, and in the process, cross-fertilize (transfer) pollen from the male anther of one flower to the female stigma of another. The high proportion of beetle-pollinated systems within the Magnolia family has perpetuated the long-standing theory that modern flowers were derived largely from beetle-pollinated proto-angiosperms. Indeed, many paleobotanists have devoted their attention to plants such as magnolias in their attempts to unravel the events of angiosperm evolution. 
    Magnolia's ancestral floral characteristics include: its large blossom with its tepal structure (magnolia's petals and usually green sepals in higher plants all look alike); its central, cone-like receptacle of spirally-arranged, male stamens at the base and similarly-arranged spiral, female carpels; its radial symmetry; its actinomorphism (floral parts similar in size and shape); and its leathery beetle-durable petals. 
    One of many botanical classification systems, Cronquist's interpretation assigns magnolias to the most archaic positions of all living angiosperms, the subclass Magnoliids, along with water lilies and buttercups. The concept that magnolias are amongst the most basal angiosperms has been refuted by higher-level phylogenetic analyses, yet they remain one of the most important lineages in the early radiation of angiosperms. Appearing long before the radiation of flowering plants, Charles Darwin called their abrupt appearance in the fossil record “an abominable mystery.” What's more, the magnolia qualifies as a "living" fossil, having changed little since it first appeared.
    By the way, magnolias acquired their name from the 17th century French botanist and physician Pierre Magnol. Now back to enjoying spring in Boston!  
    Luxuriating in the Grenville-Age High Peaks of the Adirondacks
    This High Dynamic Range photo of glacial Heart Lake was taken from the summit of lowly Mount Jo in the High Peaks region of the Adirondack Mountains in uppermost New York State. The tall peak to the right is Algonquin. Colden is the rock slide-scarred summit in the center, and to the left, Mount Marcy is the highest in the state, each separated by Precambrian faults re-activated during the Paleozoic.
    We see almost two billion years of geological scenery in the making, beginning with the meta-anorthosite bedrock that emplaced during the Grenville orogeny. The protracted, multi-phasic tectonic event culminated with the formation of the Late Proterozoic supercontinent of Rodinia and a transglobal Grenville Mountain spine. Rodinia’s subsequent fragmentation in the latest Proterozoic formed two megacontinental siblings: smaller equatorial-positioned Laurentia and larger australly-located Gondwana. The two incrementally re-assembled throughout the Paleozoic into the supercontinent of Pangaea along with its Appalachian Mountain spine.
    In the Late Cretaceous, the peneplaned Grenville’s, now internal to Laurentia, began to dome upward triggered by the region's proximity to the Great Meteor Hotspot that tracked southeastward from Canada beneath the drifting North American plate. The hotspot crossed the Mid-Atlantic Ridge, after tracking beneath the North American plate generating seamounts in its path, and is currently off the coast of Africa beneath the African plate.

    Having been glacially sculptured during the ice ages of the Pleistocene, the Adirondack’s ascent of “new mountains from old rocks” (namely Grenville basement crust domed into a mountain range) possibly continues to this day. What’s more, we geologically recognize that the Adirondack’s (located cratonward) are distinctly non-Appalachian in origin (paralleling the coast)!
    A Summer’s Wade in the Late Cretaceous Marl of Big Brook

    This lazy stream, a “piddly little dribble” in the words of the New York Paleontological Society's field guide, courses through one of the oldest and prolific collecting sites for marine fossils on the East Coast. Collectors, both amateur and professional, have been extricating both vertebrate and invertebrate faunal remains out of the clear-flowing waters of Big Brook in Monmouth County of coastal Central New Jersey for well over a hundred years.
    The diverse, age-spanning list includes Cretaceous bullet-shaped belemnite guards (a squid-like mollusc), brachiopod, oyster and clam shells, steinkerns (shell casts), hadrosaur (washed down from the mainland), shark and mosasaur teeth, alligator scutes, Pleistocene sloth and mammoth remains, Holocene Lenape arrowheads and even Colonial nick-knacks such as smoking pipes and pottery.
    As the brook wends its way to the sea through farmlands, forests and the gentrified estates of rural New Jersey, it flows through a Late Cretaceous continental shelf setting and dissects its way down through Pleistocene and Holocene alluvial surface-overburden along the way. Although the banks are off limits for active fossil exploration, the brook does most of the work for fossil hunters as the bounty virtually collapses in from the upland Navesink Formation and glauconitic Mount Laurel Formation of the streambed. All that’s needed to sift through the streambed is a wire-mesh screen, a garden trowel, a pair of waders and a little patience.
    Simply park your car, stroll a short distance through the woods, step into the stream, and travel back in time 66 to 70 million years near the end of the Age of Dinosaurs! 

    Monster Mushrooms in Chestnut Hill, Massachusetts

    This astounding three-foot beauty appears like clockwork every August near the base of a massive oak in my Boston suburb of Chestnut Hill. The rather drab, cream-colored mushroom is intricately branched with overlapping caps, yet surprisingly emanates from a single stalk. Its mycelial network remains dormant beneath the soil until summer rains and heat cause the fungal “roots” to germinate into a gargantuan “plant” above the soil. It gives the impression of growing from the ground, but it actually has colonized the buried roots of the tree, making it parasitic.
    Once considered to be plants, with which they share many traits, fungi actually belong to their own kingdom of classification. As for the mushroom (the fruitbody), it’s relationship to the parent fungus is as the apple (the fruit) to the tree. This Bondarzewia berkeleyi is a bracket fungus, so called because many within the family grow shelf-like from the sides of trees. Its reproductive spores are manufactured within tiny tubes on the underside of the fruitbody rather than within the more accustomed gills we're used to seeing. For this reason, species within this group are called polypores. If cut when fresh, the pores exude latex. It’s not considered edible because of its leathery and woody texture, not that you're tempted.

    My Lofty Visit to an Alpine Bog in New Hampshire

    Artificially located above the treeline due to ravaging fires in the early 19th century and below the climatic treeline of higher mountains in the region, this exquisite alpine bog hides on a corner of the summit of Mount Monadnock at the foot of the White Mountains of New Hampshire.
    The tops of mountains, where the climate is cold, windy and rainfall is scant, are amongst the harshest biomes on our planet. Only a select few plants and animals can exist in these severe conditions. Depressions in the bedrock collect rain and retain what little soil exists on the summit, keeping it permanently saturated. The lifeforms encountered here are similar to those found in the arctic tundra further north. Well-adapted to the bog’s poorly-drained, nutrient-poor and acidic peat soil are Sphagnum mosses, which form a carpet on which the bog’s dwarf shrubs and herbs grow. Look for Deerhair bog sedge, sheep laurel and tufted cotton-grass interspersed with patches of Labrador tea, leatherleaf, cranberry and round-leafed sundew to name a few. 
    Mount Monadnock’s rocky core at higher elevations is composed of highly metamorphosed schists and quartzites of the Devonian-age Littleton Formation, which extends well north into the White Mountains of New Hampshire. The mountain represents an overturned syncline derived from compressional forces exerted during the Acadian orogeny, the second of three tectonic collisions that created the northern Appalachians and contributed to the crustal growth of Laurentia (proto-North America).
    As our planet experiences progressively warmer climatic conditions, alpine flora and fauna will be challenged as they attempt to progress to a higher elevation to survive. They can only climb so high before being eradicated from their biome. If changing climatic conditions regionally prevail globally, the lifeforms will become extinct. This occurrence, species extinction, has been going on naturally since life appeared on our planet, but we understandably become concerned when its thought to be anthropogenic (man’s fault).
    Henry David Thoreau spent some time on Monadnock in the mid-1800's, writing in his journal about the regional botany and geology. There's supposedly a bog up here named for him. This might be it!

    High Atop Laccolithic Katahdin in the Remote North Woods of Maine
    Congratulations are in order! You’re approaching the flat Tableland of mile-high Mount Katahdin in the wilderness of northern Maine from its west flank. Notice the botanical succession you've witnessed with elevation: deciduous hardwoods in autumnal splendor that blanket the lowlands; evergreens foresting the mountain's slopes; and alpine tundral sedge in the foreground.
    The bedrock of Katahdin is a Devonian-age laccolith that has achieved its lofty status through intrusive buoyancy, surface erosion and post-glacial isostatic rebound. Katahdin (Mainers and climbers in the know drop the “Mount” from the name) formed during the Acadian orogeny, the second of three tectonic collisional phases that built the Appalachian Mountain chain and contributed to the crustal growth of Laurentia, the Paleozoic continent of North America.
    Once Pangaea fully assembled following the third orogeny, the Appalachians graced the supercontinent with a Himalayan-esque mountainous backbone. The pluton of Katahdin, along with the other regional peaks, emplaced within a sea of Late Silurian rock during the Acadian collision in what is thought to have been a retro-arc setting.
    Getting here was no easy task, especially if you just trekked 2,180 miles along the Appalachian Trail from Springer Mountain in Georgia to this point at the trail’s terminus. But you're not quite finished. To reach the Tableland you still have to complete the “A.T.’s” final assault via the Hunt Trail’s Spur on a near-vertical, 
    quad-burning, heart-pounding, lichen-encrusted, truck-sized boulder-strewn ascent of pink Katahdin granite. Once on the Tableland's plateau, you must strive for Katahdin’s penultimate summit of Baxter Peak, one of five that rim its three cavernous glacial cirques on its east flank.
    "Press on. You’re almost there. The view is spectacular!”

    The Remnants of Historic Fort Bowie within the Apache Pass Fault Zone

    Apache Pass is a natural opening and low point at the juncture of the Dos Cabezas and Chiricahua Mountains in southern Arizona. Since prehistoric times, it’s been of importance to humans as a major travel route connecting the San Simon and Sulphur Springs Valleys.
    Part of the Basin and Range physiographic province of southeastern Arizona, the surrounding mountains rise abruptly like islands of rock in an arid desert from relatively flat, sediment-filled basins that formed during an extensional tectonic regime about 20 million years ago. Even older is the Apache Pass fault zone, initiated over a billion years ago as strike-slip and more recently reactivated as normal faults during Basin and Range extension. Precambrian rocks on the southwestern side of the fault (on this side of the fort) have been moved upward relative to the Paleozoic and Mesozoic strata on the northeastern side (the hills just beyond the fort). Thus, the fort rests on Permian Horquilla Limestone of the Naco Group, while, amongst other rocks, the hills are Late Jurassic to Cretaceous Glance Conglomerates of the Bisbee Group. Erosion of the fault zone's shattered rocks formed the saddle of Apache Pass.

    The Apache people, who arrived in America with their Navajo cousins sometime after 1000 AD, hunted and camped in the area, and drank from Apache Spring that emanates within the fractured and faulted rocks within the fault zone. With the arrival of the Anglos in the mid-1800’s, Puerto del Dado, the Spanish name for the “Pass of Chance”, became the site of Fort Bowie (actually the second) by 1868 to insure the safe movement of the Butterfield Overland Mail, a stagecoach and mail service that connected Memphis and St. Louis with San Francisco. Prior to this, the arduous route was by ship across the Gulf of Mexico to the Isthmus of Panama, and on to California via the Pacific Ocean. For years, the Apache Wars led by Cochise and later Geronimo of the Chiricahua Apache waged upon the U.S. military. It all ended in 1886 with Geronimo's surrender and expatriation to Florida, leaving the foundations of the fort to decompose into the landscape.

    The region’s complex geologic history contributed to the strategic importance of the pass and delivered dependable water into the fracture zone. It's another reminder of the importance of geology and geographic setting in shaping the course of civilization and human history.

    A Six Hundred Million Year Old West African Riverbed in Newton, Massachusetts

    Oblivious to most passersby alongside Beacon Street, a major thoroughfare out of Boston, is a cross-section of an ancient streambed embedded within a cliff wall. The stream bed appears as a semi-circular channel outlined perfectly by fallen leaves. The transected bed and its banks consist of fine-grained, thinly-bedded, fissile (easily split along its planes) siltstone (mud rock) that displays a large infill of conglomerate rock over its entirety. The siltstone preserves the contours of an ancient landscape that was buried by subsequent deposition.
    Upon close inspection, laminations within the streambed display whorls of sediment indicative of stream turbidity currents and slump features indicative of settling. The manmade wall at the top is composed of stacked conglomerate boulders.
    The flat-lying rocks of the entire assemblage, being sedimentary, were deposited horizontally under the action of gravity. Subsequent to their deposition, compaction, cementation and lithification (conversion to solid rock), the assemblage and the rocks in the region were tilted by tectonic forces, which accounts for the angulation seen in the photo. These rocks belong to the Roxbury Conglomerate, a 2,000 foot thick formation of coarse arkosic sandstone with small to medium-size, rounded clasts (rounded fragments of stones). In 1830, the American poet Oliver Wendell Holmes likened the Roxbury to puddingstone, its common name, since it reminded him of raisins in English bread pudding.
    The puddingstone's sandy matrix and rocky inclusions indicate they were deposited in a high-energy depositional and/or transport system such as a cascading mountain stream or a massive submarine flow. The Roxbury is exposed almost everywhere in the neighboring towns to the west and southwest of Boston. The channel's siltstone is a facies change, a clastless sediment within the Roxbury Formation. Along with the Cambridge Argillite (or Slate), the Roxbury Conglomerate comprises the sedimentary strata of the Boston Bay Group. As mentioned in the first vignette at the top of this post, the group was deposited on the microcontinent of Avalonia in an extensional regime, such as a faulted rift basin in Late Proterozoic-time between 595 and 540 million years ago.
    Avalonia originated as an elongate volcanic island chain along the edge of the megacontinent of Gondwana, possibly of West Africa cratonic provenance in the southern hemisphere. Avalonia’s deeper basement is volcanic in origin, and, in the vicinity of the Boston Basin, they include the Brighton, Dedham, Mattapan, Lynn and Westwood granites, which underlie the rocks of the Boston Bay Group. During the Acadian orogeny, Avalonia welded to the continent of Laurentia about 370 million years ago. Can't get enough of the Roxbury Conglomerate? Check out my previous post here.

    The "unnoticed" streambed is an example of my masthead statement at the top of my blog. "Geology is all around us, scarcely thought of as we go about our lives." Perhaps I should add, "but not by all of us!"

    Happy New Year from Franklin the Border Collie (and Jack)!

    High Dynamic Range digital photograph

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    In my first post on the Great Unconformity, Part I (here), I discussed its contiguous stratigraphy within the Grand Canyon. In my second post, Part II (here), I offered a more global interpretation of the contact. In this post, I discuss the time gap at Baker's Bridge in southwest Colorado and the Great Unconformity's hypothesized significance to biological evolution.

    If you follow the Animas River some 14 miles upstream from Durango, Colorado, you’ll arrive at Baker’s Bridge in the southern foothills of the San Juan Mountains. The short bridge traverses the amazingly green-hued waters of small but strikingly scenic Animas Gorge, formed by erosion-resistant, varnish-stained walls of pale brownish-red Bakers Bridge granite. The region's beauty is a compendium of almost two billion years of geological evolution.

    Animas Gorge from atop Baker's Bridge looking north

    On this hot summer’s day throngs of locals were sunning, swimming and jumping from the bridge in what has been described as a right of passage in these parts. Chances are you won't notice (I didn’t) that this locale was used in the filming of the escape scene in the 1969 movie "Butch Cassidy and the Sundance Kid." The two leaders of the Hole-in-the-Wall Gang are cornered on a cliff by the approaching posse and make a dramatic, expletive-echoing leap to freedom from a ledge of Bakers Bridge granite into the Animas Gorge.

    Camera magic made the cliff appear higher than it really is, as Robert Redford and Paul Newman leaped into the Animas, purportedly photographed somewhere in California. Hollywood has never been concerned with geological correctness, as every geologist knows. Here’s the jump scene from the movie. Check out the Bakers Bridge granite.

    Robert Redford and Paul Newman making a leap from Bakers Bridge granite

    We're not here for a photo op or to take the plunge. A stone's throw from the bridge, our draw is geological. Where Precambrian and Paleozoic rocks are in contact, there exists a temporal discontinuity or gap in time of enormous proportions. It's on the order of 1.2 to 1.3 billion years - 25% of the earth's history missing from the geological record. It's called the Great Unconformity, distinguished with capital letters by geologists in honor of its immensity. It's at Baker's Bridge, yet it exists globally, providing you know where to look.

    The Great Unconformity at Baker's Bridge just west of the gorge

    The Great Unconformity at Baker's Bridge spans the contact between underlying medium to coarse-grained igneous rock of late Early to early Middle Proterozoic (~1700 Ma) Bakers Bridge granite. Above the contact are marine sandstones of the Upper Cambrian(?) Ignacio Formation, the Tapeats sandstone equivalent found in the Grand Canyon and on the Colorado Plateau. The question mark denotes uncertainty on the part of geologists concerning the Ignacio's age at the time of deposition. More on that later.

    Charles Baker arrived in the region with one thing on his mind - mineral wealth, but he wasn't the first to seek his fortune in the San Juans. El Dorado-seeking Spanish explored for gold deeply into the mountains during the eighteenth century, evidenced by their abandoned openings and discarded prospecting tools.
    In 1860 and 1861, Charles and his mining party established camp on the Animas River's east side. They called it Animas City (not to be confused with the later-named suburb of Durango) and built the first Baker's Bridge of logs across the narrow gorge.

    Charles Baker's bridge of logs across the Animas River (c. 1898 photograph)
    From The San Juan Highway by Frederic B. Wildfang

    Unfortunately, the prospectors found little placer gold. Deterred by hostile Utes, extreme winter hardship and the Civil War looming, the group disbanded. Charles went back east to join the Confederate forces and achieved the rank of captain. Charles returned after the war only to be killed by Utes while preparing to lead a party into the Grand Canyon. So the story goes.

    The 1870's witnessed a rush for gold in the San Juan Mountains upstream in Baker’s Park, where rich lodes were discovered. Through the 1890's, silver reigned as the predominant metal. Legend has it that Charles' cache of gold is buried somewhere in the hills around Baker's Bridge. The following memorial at the bridge recalls his trials and tribulations. The contemporary concrete bridge was built in the 1930's.

    Memorial to Captain Charles H. Baker framed in Bakers Bridge granite
    Erected by the State Historical Society of Colorado

    Discussions of the Great Unconformity invariably begin or end with mention of the spectacular display within the Inner Gorge of the Grand Canyon in northern Arizona. The contact exists between 1.7 billion year-old Early Proterozoic Vishnu Schist and overlying 525 million year-old Cambrian Tapeats Sandstone - 1.2 billion years of missing time. In Annals of the Former World, Pulitzer Prize-winning author John McPhee states, "More time is absent than is represented. If a gap of five hundred million years were the right five hundred million years, it could erase the Grand Canyon."

    The Great Unconformity within the Grand Canyon's Inner Gorge
    The time gap within the contact is 1.2 billion years, more time than it took to form all of the canyon's layers.

    John Wesley Powell, Civil War general, geologist, explorer and head of the U.S. Geological Survey, documented the Great Unconformity during his first trip through the Grand Canyon in 1869, but at the time couldn't have fully appreciated its enormity and age. We know a great deal more about the events associated with it, yet since its recognition the Great Unconformity has remained something of an enigma. Scientists enjoy torturing themselves with questions about how it formed and what happened during the long interval geologically and biologically.

    The passage of time is recorded in the rock record with deposition that might seem to occur without interruption, layer upon layer in a continuous sequence. But our dynamic planet forms new layers of rock at its surface with fits and starts, while older ones are inexorably worn away, and later redeposited upon. As a result, a hiatus or interruption within the rock record is the norm and is measured by missing time. Time isn't really missing; the anticipated rock layers are.

    Gaps in the rock record are called "unconformities" and represent rock layers that either never formed or were eroded away. The "interruption" in the depositional sequence brings strata into contact of different ages. Many are long-term gaps - tens of millions to hundreds of millions of years. The vastness of the Great Unconformity qualifies it as a unique geological entity, but as we shall see, not just because of its size. 

    Artist’s sketch of an unconformity near Edinburgh discovered by James Hutton in 1787
    The landscape erodes into a seafloor limestone that buries an older “puddingstone” conglomerate that had eroded from a mountain long gone. Below the unconformity lies a buried erosion surface of a “once mountain proclaimed below” by its vertical, folded roots. Hutton spotted the exposure in a river cutbank in Scotland.
    From by Hugh Rance

    Knowing how the gap in the rock record formed may provide important clues about crustal activity or movement such as uplift, erosion and subsidence. Thus, the "time gap" can be of tremendous geological value...even biological value!

    Horizontal strata resting atop the eroded edges of inclined strata was recognized in the early 1700’s as an indication that a significant period of erosion and non-deposition had occurred before the younger formation came to bury the older formation. In 1788, James Hutton of Scotland, the "Father of Modern Geology," looked into the abyss of time at the angular contact at Siccar Point along the northeast coast of Scotland, arguably one of the most important geological sites in the world. He described it as “a beautiful picture of a junction washed bare by the sea” and envisioned the process as an endless succession of deposition “with no vestige of a beginning, no prospect of an end,” a famous phrase in geology.

    The contact gave evidence to Hutton that deep burial of an erosion surface had occurred after prolonged erosion. His vision was limited to the realization that uplift had raised the land and was unable to see the mountains that had once existed. It wasn’t until 1805 that Prof. Robert Jameson of Edinburgh University called the surface separating two discordant formations an “unconformity.” Since then, American geologists expanded upon the entity, adding new definitions and interpretations.

    In the inset, “the uppermost sedimentary formation oversteps the erosionally truncated, upended, strata of the overlying schistus formation; itself older than apophyses of an inferred underlying body of granite.”
    The buried erosion surface is analogous to the unconformity examined by Hutton.
    Modified from by Hugh Rance

    Geologists categorize an unconformity based on the strata that embrace the contact above and below. Disconformities are found between horizontal sedimentary layers. Angular unconformities are between underlying metamorphosed, tilted and uplifted strata and overlying horizontal strata. Nonconformities are between younger, overlying sedimentary rock and older, underlying igneous or metamorphic rocks. At Baker's Bridge, igneous and metamorphic rocks below the Great Unconformity and sedimentary rocks above identify the contact as "nonconformable."

    The three types of temporal stratigraphic gaps

    Baker's Bridge resides in southwest Colorado in the southern foothills of the San Juan Mountains, whose area embraces about 12,000 square miles, the combined size of Massachusetts and Connecticut. The San Juans are a high and rugged range of the Southern Rocky Mountain province that geologist and author Donald L. Baars refers to as the "American Alps."

    Replete with alpine crags, glacially carved valleys and deep canyons, many of the peaks in the central San Juan's exceed 13,000 feet, and a few exceed 14,000. Composed of erosion-resistant granitic and quartzitic rocks, the range falls within the Colorado Mineral Belt, an area with abundant ore deposits, notably gold, that played an integral role in the region's settlement history. The San Juan Mountains contain numerous sub-ranges such as the Needles, the Grenadiers and the La Platas.

    Lofty and angular Needle Mountains under threatening summer skies
    Along the southwestern edge of the San Juan Volcanic Field, the Needles preserve evidence of the oldest mountain-building event in the San Juans. The Irving Formation and Twilight Gneiss are remnants of Precambrian-accreted, oceanic plate-derived, magmatic-arc mountains between 1.8 and 1.75 Ga. The crustal block was annexed to Laurentia in a regional tectonic event called the Yavapai orogeny.

    The San Juan Mountains possess an extremely complex history, beyond the purview of this post to elucidate. Simply stated, they are the erosional remnant of a large composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time, about 30-35 million years ago, in Colorado and adjacent parts of New Mexico. Notice Baker's Bridge (red dot) in the foothills.

    Geologic map showing the principal rock units of the San Juan Mountains in southwestern ColoradoLocate Durango and Baker's Bridge (red dot) for reference. The San Juan Volcanic Field's more recent Late Cretaceous to Tertiary volcanic and intrusive rocks rest on earlier Paleozoic and Mesozoic assemblages that in turn lie on a foundation of Early to Middle Proterozoic rocks.
    Modified from the Geologic Map of the Hermosa Quadrangle, Colorado Geological Survey, 2003

    Beginning in the latest Jurassic, subduction of the oceanic Farallon plate beneath the North American plate was responsible for east-directed compression that added crust to western North America. With ongoing subduction, compression wrinkled the Rockies skyward and uplifted the Colorado Plateau en masse, a physiographic province with minimal deformation and a handful of small volcanic intrusions in the region of the Four Corners.

    Triggered by a change in the geometrics and speed of Farallon descent into the mantle during the Tertiary, extension followed compression. Still intact internally, the Colorado Plateau's surrounding regions were extensively faulted, intruded by pluton-forming magma and covered by volcanic deposits. The outcome on the landscape was the formation of the Basin and Range province and the generation of voluminous lava on three sides of the Colorado Plateau, one of which was within the San Juan Volcanic Field on the east.

    Overstated in its simplicity, this schematic of the changing geometry of Farallon plate subduction beneath the North American plate offers one interpretation of the development of the western landscape from compression to extension.
    Modified from unknown source

    Today, the eastern boundary of the Colorado Plateau (wide black line) makes a curious skirt to the west to exclude the uplifted igneous and metamorphic rocks of the San Juan Volcanic Field (red). In Plateau Magazine (Volume 6, 2007), geologist and author Wayne Ranney states, "It is interesting to note that these volcanic deposits were erupted upon and rest on a Plateau-like surface; prior to 30 million years ago, the area of the present-day San Juan Mountains could have been considered a part of the Colorado Plateau.

    Distribution of volcanic and igneous centers (shaded gray) around the margins of the Colorado Plateau
    The San Juan Volcanic Field is shaded in red, outside the Plateau's physiographic boundary.
    Modified from Geology of the Colorado Plateau from Foos and after Hunt, 1956

    If it wasn't for late Cretaceous plutonic and late Tertiary volcanic activity that typifies the region, the San Juans would likely be included within the Plateau's eastern boundary. If you know the Colorado Plateau's Precambrian basement and its Paleozoic through Mesozoic stratigraphy, the rock units at Baker's Bridge will be fairly familiar. Later in this post, we'll briefly tap into that knowledge base for our discussion of the Great Unconformity at Baker's Bridge, in particular the strata that formed above the unconformity. First, let's visit the river that flows through Baker's Bridge.

    Perhaps prophetic, Spanish explorers in the mid-1700's named the river El Rio de las Animas Perdidas. Its 126-mile descent headwaters at an elevation of 11,120 feet in the mining ghost town of Animas Forks, over forty canyon-cut, river-miles upstream from Baker's Bridge in the heart of the San Juans. Fed by a host of tributaries, the Animas watershed drains much of the southwestern San Juans.

    The Silverton Caldera and the Animas River
    Twelve miles downstream from its source at Animas Forks in the heart of the San Juans, the Animas courses through the historic mining boomtown of Silverton at an elevation of 9,318 feet. Silverton resides within "Baker's Park", who entered the region in 1860 and 1861 in search of gold. Silverton is synonymous with the Sunnyside Mine, one of Colorado's largest. We're within the Silverton caldera, one of 20 or so in the region that formed when stratovolcanoes collapsed into their violently-evacuated magma chambers in the mid-Tertiary (35 to 30 million years ago). Radial and concentric faulting served as plumbing for upward migration of hot, acidic, mineral-laden waters. Hydrothermal solutions were charged with gold, silver, lead, zinc and copper that leached from surrounding rocks and percolated upward. Reduced temperature and pressure encountered as the ore-fluids neared the surface within the host rocks precipitated their bounty within the faults as veins.

    Suspended in time
    Obscure mine addits (entrances) that lead to underground veins are springled all over these hills, located by the tailings (waste rock) that emanate downslope from them. Today, the mines are silent with the exclusion of tourists that visit them. As the price of metals fluctuate in the market place, Silverton's dormant mines could reopen ending another cycle of "boom and bust." Stretching between the Mayflower Mill (built in 1929) and its mines (one of forty), an aerial tram's bucket still dangles against the backdrop of 13,000-foot Galena Mountain, one of several that rim the Silverton caldera. Of all the innovations introduced to the mining industry, it was one of the most important. With severe winters and the majority of the mines above timberline, trams allowed year-round work by delivering ore down to the mills, and transporting miners to and from the mines.

    Engineer Mountain
    From the San Juan Skyway (U.S. 550), Engineer Mountain is just a few feet short of being a "13er." It's roughly halfway between Baker's Bridge and Silverton, eight miles west of the Animas River. Recalling the San Juan's excluded relationship from the Colorado Plateau, Engineer displays a section of late Paleozoic, plateau-typical rocks. Cyclic marine sediments of the Pennsylvanian Hermosa Group form Engineer's forested lower slopes, while terrestrial Pennsylvanian and Permian Cutler redbeds form higher slopes, a reminder of the Ancestral Rocky Mountains (the Uncompahgre uplift specifically) that once towered over the region to the north. The light-colored, cliff-forming, columnar-jointed, intrusive sill of quartz trachyte that rimrocks the summit is likely of Late Cretaceous or early Tertiary origin. While intrusive igneous bodies were travelling through the earth's crust in the San Juan's high ranges, sills forced their way into sedimentary strata such as at Engineer. Between the Cutler and the sill is a region-wide contact known as the "Telluride erosion surface" formed during the Eocene. It bevelled the San Juan dome, a Laramide-age, basement-cored uplift, by eroding its flank. Talus on lower flanks is composed of sill material, especially the large, downslope-migrating rock glacier on the cirqued north slope out of view. Glacial thickness in this region during the Pleistocene is estimated between 2,500 and 3,000 feet but spared Engineer's summit making it a nunatak, an Inuit word. Glacier's that originated in the San Juans bulldozed through Baker's Bridge and down the Animas Valley to Durango.

    As the Animas courses south towards Baker's Bridge, its gradient varies from moderate to steep, slicing through narrow, forested canyons carved into the San Juan's erosion-resistant granites and quartzites. The Baker's Bridge granite is exposed for a few miles above the bridge within Animas Canyon.

    Sadly, the upper reaches of the Animas are contaminated by toxic heavy metals of lead, cadmium, copper, manganese, zinc and iron that discharge from the countless mines and tailings (waste) piles in Baker's Park, legacies of the gold and silver that lured the hordes of prospectors and miners beginning in the last quarter of the nineteenth century. The degradation in water quality has adversely impacted all forms of aquatic wildlife, although further downstream, particularly below Baker's Bridge, its quality is greatly improved through dilution from inflow of high quality tributaries.

    Animas Canyon
    Railroad transportation opened the San Juans by reaching its remote, land-locked mining towns and getting ore downriver. In this William Henry Jackson photo made into a 1906 postcard, the Durango & Silverton Narrow Gauge Railroad, founded by the Denver & Rio Grande Railway in 1881, follows the Animas Canyon upriver to Silverton. In continuous operation for over 130 years, the train is a popular tourist attraction, National Historic Landmark and feat of nineteenth century engineering. It's also a great way to see the remote geology within the canyon. Notice that the Needle Mountains upstream were artfully hand-colored into the photo. 

    At an elevation of 6,761 feet, Baker's Bridge (red arrow below) lies at the juncture of a profound change in the topography owing to the presence (or absence) of the locale's Precambrian crystalline basement. Above the bridge into the mountains, the Animas Canyon confines a swift Animas River within its narrow, resistant walls.

    At Baker's Bridge, where our photo of the Great Unconformity is well displayed, the Precambrian basement is in contact with the overlying Paleozoic strata. Just below Baker's Bridge where the Animas Gorge ends, the eponymous granite dives into the subsurface buried under alluvium and Paleozoic rocks.

    Animas Gorge and the upper Animas Valley
    Looking down the upper Animas Valley toward Durango from atop Bakers Bridge granite, the Animas Gorge ends abruptly where granite enters the subsurface. Immediately beyond the gorge, the channel dramatically widens, its gradient lessens and its current diminishes forcing the river to drop its sediment load. 
    These features are evident on the elevated topo-map below. The hills that frame Animas Valley are Paleozoic and Mesozoic rock assemblages coincident with those on the Colorado Plateau.

    Looking north, Baker's Bridge (red arrow) lies at the head of wide Animas Valley and floodplain and at the bottom of narrow Animas Canyon. The Great Unconformity is exposed at Baker's Bridge and for a few miles upriver. The change in terrain is at Baker's Bridge is synonymous with its granite entering the subsurface.

    Within and around Animas Valley, yellow and tan colors designate Quaternary Pleistocene and Holocene glacial, alluvial and colluvial deposits, and turquoises and shades of purple designate Paleozoic bedrock. Immediately above Baker's Bridge, the bedrock (taupe) is Paleoproterozoic Baker's Bridge Granite and Irving Formation. See references below for the on-line location of this map.

    Shaded relief map of the Hermosa quadrangle with geology and topography overlay
    Modified from the Geologic Map of the Hermosa Quadrangle, La Plata County, Colorado, 2003

    During the Pleistocene, the San Juan Mountains experienced 15 or more glacial advances that blanketed the region with a 1,900 square mile ice-field. The high cirques became ice-free at least 15,000 years ago with the peaks of some remaining above ice. The forty mile-long Animas glacier, one of the longest in the Southern Rockies, scoured out Animas Valley, evidenced by lateral moraines over 1,000 feet above the valley floor.

    Today, the U-shaped valley floor is flat, having been filled with Pleistocene glacial outwash and moraines, and Holocene alluvium (stream deposits) and colluvium (slope deposits). The valley is continually being modified by mass wasting with landslides, mudflows, debris flows and creep, and periodic Animas flooding from voluminous winter snowmelt and summer monsoons.

    The valley's walls are formed from 16,000 feet of limestone, shale and sandstone sedimentary beds of Mesozoic and Paleozoic-age. At the mouth of the Animas Valley (map below) near Durango, we ascend the Mesozoic column beginning with the Late Triassic Chinle Formation at the base of Animas City Mountain (photo below) and progress through the Middle Jurassic San Rafael Group beginning with the Entrada Sandstone. The slope-forming Late Jurassic Morrison Formation follows with a resistant cap of the Late Cretaceous Dakota Sandstone.

    We’re standing on a glacial moraine facing the mouth of the lower Animas Valley looking north across the Animas River and floodplain. Baker’s Bridge is 12 miles upvalley in the foothills of the San Juans. The valley's U-shape was scoured by the forty mile-long, Pleistocene Animas glacier that originated within the San Juan Mountains. Withdrawing late during the Pinedale glaciation, its sediments accumulated in Glacial Lake Durango, a proglacial lake that formed in a deeply scoured basin cut into bedrock. The valley's flat floor is filled with lake sediments, glacial till, and Holocene alluvium and colluvium.

    Within this expanse of the lower Animas Valley, the Ariver has become a very low energy system of oxbows and vegetation-rich, abandoned cutoffs on its flood plain. Durango, to the south behind us, is built on late Cretaceous sedimentary rock, principally the Mancos Shale, with a veneer of Animas River gravels. Higher portions of Durango are built on glacial outwash, terraces and moraines generated from the recent 18,-25,000 year old Wisconsin glacial event and others earlier such as the Pinedale.

    Mouth of the Animas Valley, Animas City Mountain and the Animas' floodplain and oxbow lake
    Animas City Mountain, across the valley, is capped with Late Cretaceous Dakota Sandstone with white Entrada Sandstone mid-slope and Upper Triassic Chinle Formation (called Dolores locally) at its base. The formations dip southwest about 7º towards the San Juan structural basin, observable in the subtle tilt of Animas City Mountain's strata. As one travels upvalley and up the dip-slope, one encounters increasingly earlier assemblages that reveal Mesozoic and then Paleozoic strata. After the Chinle, earlier deposited Lower Permian Cutler Formation is revealed, and so on. By the time Baker's Bridge is reached we're stratigraphically into the Devonian Period with majestic cliffs in the Permian Hermosa Formation surrounding the valley.

    At Baker’s Bridge, down-section in the upper Animas Valley, an early to middle Paleozoic assemblage is revealed, Cambrian(?) through Pennsylvanian. This photo was taken from atop an elongate ridge of Leadville Limestone (a Redwall equivalent) and a patchy, paleosol-veneer of reddish Molas Formation. Underlying it is Devonian Ouray Limestone that forms the cliff above the Great Unconformity at Baker's Bridge nearby.

    Looking to the northwest, Middle Pennsylvanian Hermosa Group cliffs (the type-section) dramatically rise with forested, lower slopes in the Paradox Formation. Recall that although we are positioned outside the physiographic boundary of the Colorado Plateau, the stratigraphy is Paleozoic-Mesozoic syn-depositional and concordant. The entire display is beautifully exposed throughout the Animas Valley.

    Hermosa cliffs above Baker's Bridge

    The Great Unconformity is the expression of geological events that occurred globally; that is, conditions existed worldwide to promote the development of this massive gap in time. At Baker's Bridge, the stratigraphy embracing the unconformity is an outcome of regional tectonic controls, in many respects, a microcosm of the global event.

    Acquisition of Proterozoic crust...
    The Southwest's oldest rocks, its crystalline basement, formed in a flotsam and jetsam of tectonic collisions of juvenile volcanic arcs and marine basins during the Early to Middle Proterozoic. In succession, first the Mojave, then the Yavapai (1.8-1.7 Ga), and finally the Mazatzal (1.7-1.65 Ga) provinces collided with pre-2.5 billion year old rocks of the Archean Wyoming Province of the Canadian Shield, a portion of the craton or ancient nucleus of the nascent North American continent to the north.

    Using Southeast Asia as a modern analogue, the Southwest may have appeared something like this during the Early to Middle Proterozoic. The region of Baker's Bridge (encircled) received crust largely from Yavapai tectonic derivatives.

    Rodinia's Archean core hosts tectonic convergence and crustal growth during the Middle Proterozoic
    This scenario illustrates an early stage of crustal growth at the southwest margin of the supercontinent of Rodinia. For reference, note the outline of the states. The Mojave province previously accreted to the Wyoming province (the continent's Archean cratonic) followed by Yavapai and Mazatzal oceanic magmatic arcs. Southwest Colorado at Baker's Bridge received largely Yavapai crust.
    Blakey, R. C., 2012, Paleogeography and paleotectonics of Southwestern North America:
    Colorado Plateau Geosystems, DVD Flagstaff, Arizona.

    Once accreted, the Yavapai basement in the region of Baker's Bridge and the future San Juan Mountains were twice metamorphosed during the Middle Proterozoic. The first epsiode was part of a mountain-building event called the Boulder Creek orogeny (1.72 to 1.667 Gma) in which Twilight Gneiss metamorphosed from andesite and the Irving Formation from basalt. By 1.5 Gma, the eroded Boulder Creek Mountains were covered by marine sediments of the Uncompahgre Formation.

    The emplacement of the Baker's Bridge granite...
    During the second, milder metamorphic episode of the Silver Plume orogeny (~1.5 Gma), magma intruded the Twilight and Irving metamorphic rocks with felsic plutons of both Baker' Bridge and Tenmile granites (part of the statewide Routt Plutonic Suite), and metamorphosed the Uncompahgre sediments into quartzites, slate, phyllites and schist. These Precambrian rocks can be found in the various sub-ranges of the San Juan's.

    Rifting to drifting to exposure and weathering...
    In the late Middle Proterozoic (1.4 to 1.0 Ga), the supercontinent of Rodinia finally assembled with the Grenville orogeny that united the majority of the world's landmasses and built a transglobal Grenville mountain chain. Following Rodinia's break-up in the latest Proterozoic, its crust distributed globally with the drifting apart of its continental siblings. Once exposed, the basement rock experienced extensive weathering over a prolonged period. The eroded Precambrian crust, both Archean and Proterozoic, is the foundation on which the Great Unconformity formed.

    The remnants of Rodinia's Archean and Proterozoic crustal core are distributed throughout the globe after the continents reassembled at the end of the Paleozoic into the supercontinent of Pangaea, and then redistributed upon its fragmentation.

    World map with terranes of Precambrian Archean and Proterozoic crust
    Dark areas are Archean crust: unshaded with numbers. Proterozoic crust: shaded lines in areas either under ice or preventing direct access. Phanerozoic orogenic belts: dot pattern. Proterozoic terranes are divided into three categories: 1 (confirmed), 2 (incomplete analysis) and 3 (exposed but unconfirmed).
    Modified from Proterozoic Crustal Evolution by K.C. Condie, 1992.

    Great floods of the Phanerozoic...
    On the short term, the level of the sea rises and falls, whether lunar orbitally-induced or regionally weather-related. Sea level also possesses a long-term oscillation that typically lasts hundreds of millions of years, related to celestial parameters (that trigger glaciation cycles) and planetary tectonic events (that change the holding capacity of ocean basins).

    Six times in the Phanerozoic, the level of the sea substantially rose and fell, flooding low-lying regions of the continents globally. With each landward advance (transgression) and withdrawal (regression), the seas deposited continental-scale, unconformity-bounded, sedimentary sequences. Centered on the Cambrian, the earliest was the Sauk sequence from the latest Proterozoic through the early Ordovician.


    The Sauk transgression-regression...
    At its peak, the Sauk flooded the low-lying, weathered Precambrian margins of the drifted paleo-continents and their cratonic interiors from the latest Proterozoic and into the beginning of the Paleozoic for 50 million years or so. In North America, the continent was blanketed largely with a sequence of well-sorted sandstones and clastic carbonates (excluding topographic highs such as the NE-SW-trending Transcontinental Arch that extended into Arizona and parts of the raised Canadian Shield well to the north).

    Middle to Late Cambrian paleomap of the North American Southwest
    Rising seas of the Sauk transgression bathed North America's west coast largely during the Cambrian. As water invaded the land, the shoreline eventually reached the region of Baker's Bridge. The Ignacio Formation was deposited on the Baker's Bridge granite forming the Great Unconformity at Baker's Bridge, while elsehwere in the southwest, the equivalent Tapeats Sandstone formed the Great Unconformity on uquivalent igneous and metamorphic rock.
    Blakey, R. C., 2012, Paleogeography and paleotectonics of Southwestern North America:
    Colorado Plateau Geosystems, DVD Flagstaff, Arizona.

    The birth of the Great Unconformity...
    The siliciclastic, near-shore Ignacio Formation (the Grand Canyon's Tapeats equivalent) was the first sedimentary rock deposited in the region of Baker's Bridge and the future San Juan Mountains. Voila! With covering of the Precambrian basement by the Cambrian transgressive-regressive sequence, the Great Unconformity had formed.

    The Great Unconformity, so well exposed in the Grand Canyon and on grand display at Baker's Bridge, can be traced across Laurentia (here) and found globally on Rodinia's tectonically dispersed landmasses - including Gondwana (largely the Southern Hemisheric continents), Baltica, Avalonia and Siberia. That makes the Great Unconformity "the most widely recognized and distinctive stratigraphic surface in the rock record" (Peters and Gaines, 2012). Geologists can't resist touching it and pausing for reflection!

    Sauk sequences in North America that overlie the Great Unconformity
    Distribution and age of the oldest Phanerozoic rocks in North America. Early Cambrian sediments (light gray) on the margins of the paleo-continents and later Cambrian sediments (medium and dark gray).
    Peters and Gaines, Nature, 2012.

    The Late Proterozoic and the time of the Great Unconformity was a turning point in the development of "the modern earth system" (Shields-Zhou, 2011). Its half-billion or so years were enough time to allow for a total re-invention of earth's geosphere, atmosphere, hydrosphere and biosphere.

    Geologically, it accommodated a complete reorganization of the Earth’s tectonic plates, the uplift and erosion of vast mountain ranges to sea level, a rifting apart of the supercontinent of Rodinia into smaller continental fragments and their drifting throughout the globe. Biologically, it was enough time to evolve completely new and diverse lifeforms, and accommodate their radiation.

    The two are thought to be related in that the geological processes that resulted in the formation of the Great Unconformity provided the impetus for the burst of biological diversity of the Cambrian Explosion of multi-cellular animal life. There are many competing theories that are highly controversial and lack a consensus of opinion. That said, let's attempt to assimilate them into one apologetically simplistic scenario. It's a rather unlikely tale of a fragmenting supercontinent, a dimly lit planet that became entombed in glacial ice, a hothouse heat wave, an oceanic geochemical infusion and an explosion of multi-cellular animal life within the sea.

    During the Great Unconformity, the breakup of Rodinia (900-750 Ma) occurred largely during the Tonian Period (Greek meaning “to stretch”) early in the Late Proterozoic. In the Cryogenian (Greek for "cold" and "birth") Period (850-635 Ma) in the mid-Late Proterozoic, our planet experienced two intense and widespread glaciations that were notably equatorial in locale - as opposed to more familiar high latitude Phanerozoic glaciations such as those of the Pleistocene.

    These were the Sturtian (715-680 Ma) and Marinoan (680-635 Ma) glaciations. A third Cryogenian glaciation, the Gaskier or Varanger, was less extreme, likely short-lived and not global in extent.

    The ice ages prevailed with such intensity that the surface oceans in the tropics froze. The event has been anointed with the colorful and description of “Snowball Earth” 
    (Kirschvink coined the term in 1992, and Hoffman presented the hypothesis in 1998). It’s a bold and imaginative theory that remains speculative and controversial, yet very attractive since it successfully explains the geological findings regarding the glaciations (e.g. equatorial glacial tillites and diamictites, banded iron formations, post-glacial marine “cap” carbonates, carbon isotopic anomalies, etc.).

    These events – Rodinia's assembly, break-up and the ensuing glaciation - preceded the recognition of multicellular animal life during the Ediacaran Period (named for the type-section at the Ediacara Hills of Australia), the final time period of the Proterozoic.

    What are the causes of extreme climate deterioration, that is, the prolonged cooling that led to equatorial snowball glaciations? Proposed explanations include extraterrestrial triggers such as galactic cosmic rays driving cloudiness, the dimmer young sun (solar luminosity 83-94% of present-day values) and high planetary obliquity (> 54º of axial tilt) that resulted in a colder low-latitudinal climate than at the poles. Terrestrial triggers include methane degassing from anoxic oceans (boosting the hydrologic cycle) and tectonic influences.

    The latter trigger - tectonics - relates epochs of glaciation to a reduction in the partial pressure of atmospheric CO2 caused by supercontinental break-up. It’s an attractive model. Here’s how it works.

    Rodinia fragmented apart a good 70 million years before the first snowball event. Although Rodinia may have stretched from pole to pole, its paleo-orientation and that of its rifted constituents was likely, largely equatorial, at least initially. Its fragmentation generated intense magmatic activity within the Laurentian magmatic province. It also opened many seaways as the severed continental blocks drifted apart, which in turn increased precipitation and temperature along newly rifted margins, largely in a low-latitudinal locale.

    Equatorial cluster of Rodinia's fragmented landmasses during the global glaciations that occurred during the Cryogenian Period. Our planet witnessed the continents reassemble at the end of the Paleozoic and again redisperse. Geological relics of the debris left behind when the ice melted are exposed on the contemporary land surface. Namibia (red dot) is a notable example.
    From Snowball Earth by Paul F. Hoffman and Daniel P. Schrag, Scientific American, 1999

    The continental runoff increased weathering, particularly of silicates on freshly generated basaltic surfaces, and hence atmospheric consumption (q.v. long-term carbon cycle). The “drawdown” (reduction) of CO2, a greenhouse gas, resulted in long-term climate cooling, trending toward an icehouse. As ice accumulated equatorially, a “runaway ice-albedo” 
    (reflective ice reduced solar absorption leading to more cooling; Budyko, 1968) drove the earth into a snowball glaciation. Thus, supercontinental break-up is thought to have had a profoundly cooling effect at low latitudes during the Late Proterozoic and to have been the main trigger in reducing atmospheric CO2.

    The Snowball Earth hypothesis also postulates that millions of years of glaciation ended when sufficient volumes of volcanically-derived CO2 emissions accumulated within the atmosphere. Degassing overcame the effect of the runaway albedo climate, which collapsed weathering and allowed the planet to transition from an icehouse to a greenhouse world that melted the ice and liberated the planet from its snowball state.

    A geochemical infusion of weathering products...
    During the Great Unconformity, continental exposure and chemical weathering of silicate materials effected seawater chemistry and global bio-geochemical cycling in the atmosphere and the oceans. The weathered-runoff was delivered to rivers and oceans in massive quantities conducive to the evolution of new forms of life, in particular, Ediacara-type fauna that flourished as a prelude to more diverse forms of the Phanerozoic world.

    The final stages of the Great Unconformity are thought to have acted as a “geological trigger” by infusing the oceans with continental weathering products including carbonates, calcium, potassium, sodium, magnesium and iron (Peters and Gaines, 2012). That had profound implications for ocean chemistry at the time that complex life was proliferating and initiated a biochemical response seen in the Cambrian Explosion.

    Lifeforms that existed before and after the Precambrian-Cambrian boundary differed immensely. During the Ediacaran Period lifeforms were plant-like, suspension-feeding metazoans (multi-cellular) that lacked the morphological capacity (form and structure) for locomotion and were non-biomineralized (without hard calcified tissues like shells and bones).

    They are generally viewed as the oldest unequivocal animals and passive inhabitants of their ecosystem, tethered to a cyanobacterial microbial mat on the ocean floor. By and large, the Ediacara fauna became extinct by the end of the Ediacaran Period, although proponents of Burgess-type ancestral relationships believe some lifeforms persisted into the Cambrian.

    Ediacara-type fauna
    Although appearing plant-like morphologically, the Late Proterozoic Ediacara-type fauna were the first multicellular marine animals. Benthic (substrate-loving) and mostly afixed to a cyanobacterial microbial mat on the ocean floor, they lacked the capacity for locomotion, vertical bioturbination and predation.

    Following the Ediacaran-Cambrian boundary, new lifeforms were distinguished by the emergence and rapid diversification of more complex multicellular animals, by their acquisition of biomineralized skeletons (phosphate and carbonate salts of calcium), and by their innovative body plans with movable, muscular body parts.

    With new bodies came new lifestyles - possessing the ability to bioturbinate the substrate (rework the sediments by burrowing), move vertically through the water column and exploit new habitats. Predation had begun across the threshold of the gap in time, and along with it, the ability of prey to protect themselves and escape from capture. Things have never been the same. This period is referred to as the Cambrian Explosion of life because of the seemingly abrupt timing of the biological event. Evolutionary biologists single the Cambrian Explosion as the event that generated all the phyla that have persisted to the present.

    Burgess Shale-type fauna
    The Cambrian Explosion typifies a fundamental change in marine ecosystems. Ediacaran two-dimensional mat scraping was replaced by three-dimensional infaunal burrowing (within the substrate). The Middle Cambrian Burgess Shale-type fauna was empowered by the development of muscular, biomineralized body parts and innovative body plans, which not only enabled surface grazing but movement throughout the water column.
    Artist John Sibbick of Time Magazine

    Alas, we have come to perceive the Great Unconformity as more than just a gap in time but as “a unique physical, environmental boundary condition” (Peters and Gaines, Nature, 2012). Reflecting on the dramatic transition from Ediacaran to Burgess-style lifeforms across the Great Unconformity, Robert R. Gaines (personal communication, 2012) believes the "geological circumstances surrounding its formation led to the Cambrian Explosion."

    Analyses of seawater chemistries “provide support evidence for changes in tectonic activity and enhanced (and extensive Late Proterozoic) continental weathering during the formation of the Great Unconformity” (Peters and Gaines). The chemical infusion that was delivered to the sea – with minerals such as calcium that rose precipitously – has been proposed as a mechanism for the origin of biomineralization of animals during the Cambrian Explosion that evolved in Cryogenian to Ediacaran time.

    Summary of major tectonic, geochemical and sedimentary patterns over the past 900 Myr
    The wavy dark gray blob (global mean isotopic Sr) is a measure of the progressive exposure of weathering granitic continental crust required to form the Great Unconformity. The wavy light gray blob (global mean εNd) is a measure of young arcs versus old continental crust. The vertical green bars identify continent-scale sedimentary sequences particularly the Sauk transgression (the first of six global high seas during the Phanerozoic) that blanketed the Great Unconformity in the Cambrian. The vertical blue bars indicate major global glaciations during the fragmentation of Rodinia and preceding the radiation of the Ediacara-type fauna. The timing of Rodinia fragmentation in relation to the Great Unconformity is designated across the top. Following the fragmentation of Rodinia, the Great Unconformity is defined by a shift from widespread continental weathering (red bar) to widespread sedimentation (yellow bar).
    From Peters and Gaines, Nature, 2012.

    Now that we have an enlightened geological and biological perspective of the events that occured during and surrounding the Great Unconformity, let's take one last look at the contact at Baker's Bridge. The Ignacio Formation, the stratum anticipated to cap the Great Unconformity, appears absent at Baker's Bridge.

    Close-up of the Great Unconformity at Baker's Bridge
    The regional paleotopography - its ancient landscape - is indicated above the Bakers Bridge granite, where the Ignacio Formation is absent and the Elbert Formation is overlies the Precambrian basement. Elsewhere regionally in the San Juans, the Ignacio can be found overlying the contact.

    Geologists have found it difficult to distinguish between the sandstones of the McCracken from the underlying Ignacio. Petrographic analyses at Baker's Bridge has found that the sandstone overlying the Great Unconformity is more similar to the Devonian McCracken Sandstone Member of the Elbert Formation rather than the Cambrian Ignacio Formation, which contacts the granite elsewhere regionally. The following paleo-map depicts the widespread Devonian through the Mississippi-age Kaskaskia transgression (on the sequence map above) that deposited Redwall limestones in northern Arizona, and Elbert and Leadville Formations in the region of Baker's Bridge in Colorado.

    Late Devonian paleomap of the North American Southwest
    The Kaskaskia transgression, the third eustatic event to reach the Southwest in the Phanerozoic, deposited the Elbert and Leadville Formations. Where the Ignacio was absent, the Elbert capped the Great Unconformity.
    Blakey, R. C., 2012, Paleogeography and paleotectonics of Southwestern North America:
    Colorado Plateau Geosystems, DVD Flagstaff, Arizona.

    The McCracken-Ignacio age-uncertainty has persisted in the literature for over a hundred years, much to the surprise and even disappointment of some Plateau geologists that expect the Tapeats or its regional equivalent overlying the Great Unconformity. The problem has been with the precise dating of the Ignacio, which has been difficult since it's regionally depauperate (greatly diminished or devoid of ecosystem fossils). In the strata above the Ignacio, trace burrows, and brachiopod and fish remains are plentiful in the Elbert and overyling Leadville, which does allow reliable dating.

    I asked the question "What stratum overlies Baker's Bridge granite at Baker's Bridge?" to Dr. David Gonzales, Professor and Chair in the Department of Geosciences at Fort Lewis College in Durango). He responded, "Unfortunately, there is not a definitive answer (personal communication, 2013). He continued, "The Ignacio Formation at Baker's Bridge is somewhat unique on a regional level. In a number of locations, Devonian limestone lies directly on Proterozoic rocks. So, clearly, depending on what area you are in, there is both Cambrian(?) and Devonian rock units on the Proterozoic. Unless more fossils are found, I am not sure the issue will be easily resolved."

    A thesis interpretation (Maurer, 2012) of the strata-conundrum attributes Ignacio's absence at Baker's Bridge to its deposition mostly as estuarine within an incised valley sequence. Thus, it was not deposited at Baker's Bridge but located elsewhere regionally. With the return of the sea, the landward advance of the Kaskaskia transgression left McCracken marine sediments upon Bakers Bridge granite at Baker's Bridge.

    The Ignacio question at Baker's Bridge is surprising to geologists that anticipate its presence. But technically - recalling our definition of the Great Unconformity - the overlying strata can very greatly both regionally and even globally contingent on the circumstances of deposition. 


    This exposed surface of the shallow-marine Mississippian Leadville Formation displays 350 million year old, crinoid stem-ossicles, bivalve shell fragments, rugose horn corals and much later Pleistocene glacial polish and striations. It is a unique occurrence to find the Leadville Limestone glaciated compared to its non-glaciated Redwall-equivalent in the Grand Canyon.

    Back at the bridge, glacial and fluvial erosion have stripped the sedimentary cover from the granite, and allowed the Animas River to carve a channel through the Animas Gorge. Notice the smooth glacial polish and multiple, parallel glacial striations produced by the Animas Glacier moving downvalley some 18,000 years ago. Once exposed, repetitive freeze-thaw cycles have also taken their toll on the granite as it began to exfoliate at the surface into gently curved slabs.

    Ancient Landscapes of the Colorado Plateau by Ron Blakey and Wayne Ranney,
    Plateau: The Land and People of the Colorado Plateau
    , Vol. 6, Nos. 1 and 2, 2009.
    Snowball Earth by Paul F. Hoffman and Daniel P. Schrag, Scientific American, 1999.
    The American Alps by Donald L. Baars, 1992.

    The Garden of Ediacara by Mark A.S. McMenamin, 1998.
    The Geology of the American Southwest by W. Scott Baldridge, 2004.
    The Roadside Geology of Colorado by Halka Chronic and Felicie Williams, 2002.
    The Western San Juan Mountains by Rob Blair, 1996.

    Wonderful Life by Stephen Jay Gould, 1989.

    Geologic Bedrock Map of the Hermosa Quadrangle, Colorado Geological Survey, 2003.
    Reinterpretation of the Ignacio and Elbert Formations by Joshua T. Maurer, 2012.
    Petrologic Evolution of the San Juan Volcanic Field by Peter W. Lipman et al, 1978.
    Formation of the Great Unconformity as a Trigger for the Cambrian Explosion by Shanon E. Peters and Robert R. Gaines, Nature, 2012.

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    “The tops of mountains are among the unfinished parts of the globe,
    whither it is a slight insult to the gods to climb and pry into their secrets,
    and try their effect on our humanity.
    Only daring and insolent men, perchance, go there.
    Simple races, as savages, do not climb mountains,
    their tops are sacred and mysterious tracts never visited by them.
    Pamola is always angry with those who climb to the summit of Ktaadn.”
    The Maine Woods by Henry David Thoreau, 1864
    who employs a phonetic spelling of Katahdin.
    We're facing east from Baxter Peak at 5,269 feet, the penultimate summit of Katahdin's five peaks and the highest point in the State of Maine. The afternoon sun is casting long October shadows into the semi-circular abyss of glacial ice-gouged South Basin. A vertiginous 2,000 foot headwall of erosion-resistant Katahdin granite rises to the top of Pamola Peak across the cirque. To the right of Pamola and running to the summit on which we're standing is a daring traverse called the Knife Edge. It's a two-foot wide boulder-scramble on the apex of a glacial arête that is both famous and revered throughout the northeast. 
    Textbook glacial tarns, hummocky moraines and serpentine eskers lie on a heavily forested, boulder-strewn outwash plain across the valley floor. Welcome to Katahdin!
    Classic Glacial Features From Atop Baxter Peak
    This two-photo panorama was taken from the summit of Baxter Peak, one of five satellite peaks that lie on Katahdin's horseshoe-shaped rim. In the middle distance bask North and South Turner Mountains, and beyond the horizon lies the Bay of Fundy of Nova Scotia. Please click for a larger view.

    Pronounced "kuh-TAH-din", it's a Penobscot word of Maine Native Americans that means "the greatest mountain", so the need for "Mount" is redundant. Katahdin and its features harbor geological secrets of their past that have plagued geologists for over a century.

    What is the tectonic relationship of Katahdin to the Appalachian Mountain chain along North America’s eastern margin? By what tectonic design did Katahdin's granitic core emplace? How did did Katahdin come to be positioned within a middle Paleozoic “sea” of metasedimentary rock?
    Katahdin's calderic-appearing profile resembles that of Mount St. Helens. Do they share a common volcanic geo-genesis? Why does Katahdin’s granitic core become redder and more resistant to erosion with elevation?

    The granites of Katahdin and the rhyolites of nearby Traveler Mountain exhibit a remarkable chemical homogeneity and time of emplacement. In fact, a contact exists where one intrudes the other. Is there a geological association between Katahdin and Traveler Mountain? By what process did Katahdin’s subterranean magma chamber become "the greatest mountain" towering above the others in the region? 

    Great Basin by American landscape oil painter Frederic Edwin Church (1826-1900), 1852.
    Why is Katahdin’s western flank an upward slope to a high plateau, while its east side is a steep, glacier-sculpted collection of cirques? Did the Laurentide ice sheet of the Pleistocene carve all of Katahdin’s features or did alpine glaciers contribute to the job?

    Penobscot mythology exalts Pamola - part moose and part eagle - as the prisoner-taking spirit of thunder and supreme protector of “K’taadn.” Our fervent hope on this near-freezing Columbus Day weekend, the last of the hiking season in Baxter State Park of Maine, was that the mysterious winged deity would hold mountain storms, lightning strikes and high winds at bay, and repress his anger long enough for us to ascend his granite fortress, observe its geology - and return safely.  


    Baxter Peak and the Knife Edge from Atop Pamola Peak
    This view faces west from Pamola Peak toward Baxter Peak, the opposite perspective from the photo above. The hikers at the left are on a section of the mile-long Knife Edge Trail. Notice the rubble that litters the summit. This is a Wikipedia photo.

    About 90 miles upstream from Penobscot Bay in mid-coastal Maine, the Penobscot River divides into a West and East Branch. Between the two branches is the edifice of Katahdin in north-central Maine, near its geographical center at: 45º 54’ 16.07” N, 68º 55’ 18.75” W. If you plug the co-ordinates into Google Earth, it will take you there.

    Bangor is 75 miles to the southeast, and Boston is another 225. Nova Scotia and the Bay of Fundy are a good 200 miles to the east, and the Canadian border is 60 miles to the northwest towards Quebec.

    In 1836, C.T. Jackson began what would become the first field season of what was to become the first report on the geology of Maine. He ascended to the summit of Katahdin and noted that the mountain was comprised completely of granite, and that, based on the erratics on the mountain, believed it was evidence of the Biblical Deluge that had covered the mountain. Water certainly did but not in its aqueous form. Using barometric observations, he calculated the altitude above sea level to be 5,300 feet - only 31 feet off!
    From the Maine Geological Survey

    Using the simplest definition possible, Katahdin is a steep and tall mountain composed of a large mass of granite that has weathered to the surface over time. Its granite core formed within a cooled magma chamber or batholith below the earth's surface. It's also a pluton - an encompassing term that includes other intrusive (also called plutonic and means formed into older rock below ground) igneous bodies such as stocks, dikes and sills.

    When molten magma reaches the surface, it may extrude and flow as lava, or in the case of Katahdin, violently eject outward under tremendous pressure. Small particles of ash blasted aloft and settled on the landscape in the form of a rock called welded tuff when solidified. Rhyolite is the extrusive counterpart of its parent intrusive granite. Thus, rhyolite-tuff describes its chemical composition and genesis-rock, Katahdin granite.

    These volcanic events are the result of tectonic plate convergence on the earth's surface, a process that forms continents, closes intervening ocean basins and builds lofty mountain ranges. The tectonic collision that created the magma chamber of Katahdin also built the Appalachian Mountain chain. Of course, this is a basic interpretation. In order to better understand the topography, we must gain an appreciation for the geologic processes that have shaped the region and the east coast of North America for that matter.

    Katahdin is Maine’s highest mountain and lies at the northern terminus of the 2,178-mile Appalachian Trail that starts on Springer Mountain in Georgia. A trek on the meandering AT parallels the strike of the Appalachian orogen through 14 states and includes many terrains familiar to historians and terranes to geologists alike - the Cumberlands, the Blue Ridge, Shenandoah, and the Green and White Mountains of New England.

    The footpath of the Appalachian Trail from Springer Mountain in Georgia to Mount Katahdin in Maine
    follows the strike of the Appalachian orogen.
    Map from

    Katahdin is the undisputed centerpiece of Baxter State Park - an over 200,000-acre preserve of mountains and valleys generously established by donations of land beginning in 1931 from Percival P. Baxter, a two-time governor of Maine. To protect the area from logging, he personally purchased the land from logging companies and deeded it to the state.

    The stipulation was that it remains “forever…in the natural wild state…as a sanctuary for wild beasts and birds that no roads or ways…be constructed therein or thereon.” In Governor Baxter's own words: 
    "Man is born to die. His works are short-lived.
    Buildings crumble, monuments decay and wealth vanishes,
    but Katahdin in all its glory forever shall remain the mountain of the people of Maine."
    Baxter Park Rangers fastidiously preserve and protect the park and its hikers, watching the weather closely for safety and disallowing ascents in storms and high winds. The number of climbers are regulated by the number of cars allowed to enter Baxter, so arrive early with an online registration (here). During the recent federal government shutdown, my confirmation call to the park was proudly answered, “Of course we’re open! We’re a state park and independently funded at that!”
    Northern Appalachians Ablaze with Color
    Beneath overcast skies on our approach to Baxter State Park from the southeast the day before our climb,
    Katahdin's summit and those of its neighbors were shrouded in mist. Salmon Stream Lake is in the foreground. 

    Recording a billion years of orogenesis, the once Himalayan-comparable Appalachian orogen
    extends 2,000 miles from Georgia to Maine and as far as Newfoundland, Canada with buried components beneath the Atlantic and Gulf coastal plains, and the Atlantic continental shelf. Named by the Spanish in the 1500’s for a Native American tribe – the Apalachis - it is an eroded, accretionary orogen and represents the site of long-vanished ocean basins consumed in a collision of a mosaic of terranes with Laurentia - the core of ancestral North America.

    Traditional descriptions of the evolution of New England and its Northern Appalachian section include a succession of Paleozoic tectonic events: the Penobscottian, Taconic, Salinic, Acadian and Alleghanian orogenies. The landscapes that these mountain-building events created are manifested by a geological zonation across the strike of the orogen in the direction of their tectonic migration onto and across Laurentia (below).

    Unravelling the tectonic history of Laurentia's eastern plate margin has been an arduous and complicated work in progress. That said, let's briefly summarize the orogenic events in order to put Katahdin's regional emplacement into perspective (red dot).

    Regional Geologic Map of the Northern Appalachian Orogen from New York to Newfoundland
    For orientation, identify the states of New England and New York outlined with a dashed line (also inset lower right). Locate New York State on the far left with its upstate Grenville-age Adirondack Massif and downstate Acadian-age Catskill Delta. The Taconic Queenston Delta lies beneath and imprinted by the Acadian. To the east lies the Appalachian front and the many terranes that were accreted and deformed during the Paleozoic. 
    The red dot is the location of Katahdin in north-central Maine within the Piscataquis magmatic belt, an assembly of mafic and igneous rocks of Early Devonian-age (407 Ma). The belt is closely associated with coeval sedimentary rocks of Emsian age.
    Modified from Rankin et al, 2007

    In the earliest Paleozoic, the fragmented Late Proterozoic supercontinent of Rodinia is represented largely by the megacontinents of equatorial Laurentia, South Hemispheric Gondwana and the micro-continent of Baltica - all sharing the waters of the Iapetus Sea. This was a pivotal interval in the Earth’s history – a time of worldwide orogeny, proposed "snowball" glaciations, rapid continental growth, profound changes in ocean geochemistry, and an explosion of biological activity and early animal radiation (Visit here).

    Rodinia's rifted continental elements would re-assemble in succession throughout the Paleozoic and eventually form the supercontinent of Pangaea, create the Appalachian Mountain chain and emplace Katahdin in the process.

    Rodinia Shortly After its Fragmentation ~750 Ma
    The megacontinent of Laurentia is positioned equatorially. The recently rifted continents, by and large, have not yet reassembled at ~550 Ma australly as Gondwana. Orange represents 1300-1000 Ma mountain belts; green represents continents with paleomagnetic data.

    Torsvik, 2003

    Equatorial-positioned Laurentia and South Hemispheric-positioned Gondwana in the Middle Cambrian
    Laurentia, Baltica, Gondwana and sundry microplates are separated by the Iapetus Ocean. It is at this time that Avalon terranes are rifting from Gondwana.

    The Pebobscottian orogeny is in part coeval (time equivalent) with the early phases of the Taconic orogeny (below). It was caused by a collision between the Penobscot arc and the terrane of Ganderia, a widely misunderstood microterrane situated in the periphery of Gondwana across the Iapetus Ocean. It involved back-arc ophiolites that were obducted onto the Gander margin. The composite terrane trends northeast from Northern New Hampshire, across west-central Maine and into New Brunswick, Canada. This subduction-obduction tectonic event occured in the Late Cambrian to Early Ordovician and preceded the Taconic orogeny, whose arc rocks locally overlie it.

    After some 150 million years following Rodinia's fragmentation, the world's continental plates began to converge in the early Paleozoic, driven by the incremental closure of their interposed ocean basins. The first was the Late Ordovician Taconic orogeny from Newfoundland to New York. It i
    nvolved Laurentia’s collision with an island arc complex upon closure of the intervening Western Iapetus Ocean.

    The Taconic allochthon that formed signifies the earliest recognition of the Northern Appalachian Mountains in western New England and southeastern New York State, while a massive clastic wedge was shed westward into a developing foreland in New York, Pennsylvania and beyond called the Queenston delta.

    This was the beginning of the replacement of the open seas of the Western Iapetus off the coast of Rodinia with "exotic" continental crust, a process that would end in the northeast with the formation of New England, Maine and the emplacement of Katahdin. 

    The Taconic Orogeny
    In the Late Cambrian (500 Ma), the elongate Taconic magmatic arc (red arrow) converges on the Laurentian plate's passive eastern shore at the expense of the Western Iapetus Ocean. To the east, the Eastern Iapetus awaits closure with the convergence of the Avalon micro-continent. Note the Panthalassic Ocean (proto-Pacific Ocean) enveloping the remainder of the globe. The State of Maine is somewhere out on Laurentia's continental slope, and Katahdin has not yet formed.
    Modified from Colorado Plateau Geosystems. Inc.
    From Time Slices of North American Geologic History DVD

    The tectonic history of New England during the Paleozoic has been dominated by discussions of island arcs, exotic terranes and compressional events. Recently, an event of crustal extension has been elucidated - the Salinic orogeny. Replete with sedimentation and a mafic intrusive complex, it developed within elements of the Taconic event in central New England to the west during the Silurian. It includes deep-water strata of four basins, two of which are relevant to our discussion of Katahdin: the Connecticut Valley-Gaspe synclinorium and the Central Maine trough in New England and eastern Quebec.

    A boundary within the basins implies a change in the depositional setting from an intercontinental backarc extensional setting to a foreland basin as the Acadian wedge approached from the east (black arrow). Other tectonic models have been proposed, but regardless of the process, the Salinic involved rifting or crustal divergence followed by Acadian deformation and metamorphism. 

    On the "Regional Geologic Map" above (red dot) and the map below (red circle), note Katahdin within the Piscataquis magmatic (volcanic) belt AND within the CVG and Central Maine basins. Outboard in the direction of the Acadian front to the southeast (diagram below is a rotated perspective) lies Avalon's coastal volcanic belt "proper" of the orogen.

    Principal Tectonic Features Map of Maine, Eastern Quebec and Parts Vermont and New Hampshire
    Katahdin's location is within the Piscataquis volcanic (magmatic) belt amongst the Lower Devonian flysch and molasse of the CVG and Central Maine basins. Note also the location of Avalonia's coastal volcanic belt.
    The direction of migration of the Acadian front is from southeast to northwest (black arrow).
    Modified from Bradley and Tucker, 2002.

    The third event to shape northeastern Laurentia was the Middle Devonian Acadian orogeny with the closure of the Eastern Iapetus Ocean. It involved the collision of Avalonia – a peri-Gondwanan, rifted terrane - with Laurentia's east margin. It too built a large clastic wedge and foreland called the Catskill delta. In reality, the accretion of the Avalon arc involved several composite subduction zones. The details of its superterranes and geometries of the Acadian event are only partially understood and beyond the scope of this post.   

    Convergence of the Avalon Arc
    With the Taconic orogen fully developed during the Late Ordovician (450 Ma), the Avalonian and Baltican micro-plates converge upon Laurentia at the expense of the Eastern Iapetus Ocean. With each collision, mountains were built and crust was added to Laurentia - the expanding proto-North American continent. Also note the relative tectonic quiescence on Laurentia's west coast. Its marginal passivity will end when the east coast's tectonic activity ceases. Our planet is a sphere of fixed dimension. Two massive oceans (such as the Atlantic and the Pacific) can not form simultaneously. One forms at the other's expense.
    Modified from Colorado Plateau Geosystems. Inc.
    From Time Slices of North American Geologic History DVD

    The Acadian orogeny finalized the northern Appalachians from the Canadian Maritimes into New England (and the central and southern Appalachians into the Carolinas), and penetrated into, deformed and imprinted the previous Taconic orogen and its foreland. In Maine, it formed the state's highest mountains in a belt that runs from the New Hampshire border on the west through Katahdin and beyond to the northeast, a distance of 150 miles. In New Hampshire, the range continues through the White Mountains to Mount Monadnock in the southwest part of the state. Thus, the Maine Appalachians are mostly Devonian in age - initially Taconic but deformed and elevated in the Acadian orogeny.

    Katahdin emplaced during the Acadian orogeny as deformation migrated from the southeast to the northwest. What's more, its curious locus of emplacement relevant to the Acadian subduction zone was within the flysch and molasse of the Acadian foreland, which will be investigated on our climb of Katahdin.   

    The Acadian Orogeny
    Fully developed by the Late Devonian (375 Ma), the Acadian orogen accreted to Laurentia and deformed the eastern flank of the Taconic orogen. Likewise, Baltica has merged with Avalonia to its south. By this time, the Northern Appalachians have formed and Katahdin has emplaced within northern Maine. Notice Gondwana  (lower right) draws near signalling the formation of the supercontinent of Pangaea.
    Modified from Colorado Plateau Geosystems. Inc.
    From Time Slices of North American Geologic History DVD

    Lastly, the Pennsylvanian-Permian Alleghanian orogeny (Ouachita orogen in southern and eastern Mexico, and Hercynian-Variscan in southern Europe) finalized the Central and Southern Appalachians and overprinted the Acadian orogen by deforming and metamorphosing parts of New England.

    The Acadian involved a largely translational, highly oblique, continent-continent collision that closed the Rheic Ocean, sutured western Gondwana to Laurussia (Laurentia and Baltica), completed a Wilson cycle (here), produced the Appalachian Mountain chain and finalized the formation of Pangaea. The multi-phasic, Taconic through Alleghanian, Paleozoic-spanning event is summarily called the Appalachian orogeny.

    The Alleghanian Orogeny
    By the Early Jurassic (180 Ma), the Rheic Ocean between Laurentia and Gondwana had closed, and Pangaea, having fully formed, had initiated its fragmentation apart. Within the developing rift between North America, and Africa and South America, the waters of the Atlantic Ocean filled the growing void. Roughly concomitant with the initiation of a passive continental margin on Laurentia's east coast, active tectonics initiated on Laurentia's west coast. Rifting apart of Pangaea gave birth to the Atlantic and Pacific Oceans, the modern continents of the Cenozoic including North America, and the Appalachian Mountain chain along the east coast. The red arrow identifies Katahdin within the Northern Appalachians.
    Modified from Colorado Plateau Geosystems. Inc.
    From Time Slices of North American Geologic History DVD

    Following Pangaea's breaking apart, the familiar continents of our modern world took their places across the globe. The Panthalassic Ocean would become the Pacific. Laurentia's east coast became a passive margin, while its west coast became active - the site of convergence. Pangaea's fragmentation left the Katahdin pluton within the region of the Northern Appalachians of Maine, a hundred or so miles from the sea. Voila!
    Our plan was to climb Katahdin from the east, where the bedrock is well exposed for observation. It's also one of the best places to view glacial features both on Katahdin's slopes and the valley floor, so we didn’t want to miss the opportunity after having driven over 300 miles from Boston on the previous day. The entire month of October experienced heavy rain in New England, but the forecast for our climb was blue sky. We were elated.
    Katahdin from the east
    Katahdin looms large from all directions, here from the east outside of nearby Millinocket.
    High Dynamic Range photo contributed by resident Mainer FL Doyle III (
    Visitors to Baxter State Park are regulated by the number of cars that are allowed to enter. Unfortunately, having arrived only minutes late, the gate attendant gave away our reserved parking space, the last one on Katahdin’s east side. He offered parking on the west side, not our preference, which we readily accepted. Our passing thought (which eventually became our plan) was to ascend from the west and descend to the east. The problem was that it would put us over 20 miles from the car after dark.
    Before driving away from the gate, the attendant asked us a curious question, "Got a flashlight?" "Yes", we answered. More on that later. A word to the wise – don’t be late at the gate, or better, camp at the base of Katahdin the night before your climb. And don't forget that flashlight!
    Topographic Map of Katahdin
    Our route (red arrows) on Katahdin was an 11-mile, west-to-east traverse. Beginning at the trailhead at Katahdin Stream Campground, the progression was up Hunt Trail, across the summit and down by the Saddle Trail to Roaring Brook Campground via the Chimney Pond trail. Click on the photo for a larger view.
    At 5,267 feet, Katahdin is the highest mountain peak in Maine, yet it has a local relief of 4,700 feet making it one of the largest massifs (a massive mountain formed of basement or plutonic rocks) in the Appalachian Mountains. There are many routes to the summit of Katahdin, all of which involve some degree of scrambling (using all fours) and all of which are steep and challenging.
    We headed out on the Hunt Trail, a popular ascent with outstanding features (far right on Google Earth below). Notice the flat plateau on Katahdin's west side (right), and the collection of cirques on the east side (left). Download trailmaps of Katahdin here.
    Google Earth View of Katahdin Looking South

    The trailhead is at Katahdin Stream campground, elevation 1,075 feet. It follows the stream on a persistent upslope built on talus through a mixed boreal forest of hardwoods such as white birch and red maple, and evergreens such as balsam fir, red-black spruce, hemlock and white cedar. The ground flora was rich in mosses, ferns, bunchberry and hobblebush. This is an alpine temperature ecosystem of great diversity.

    Virtually all of the granite bedrock is related to the time of Katahdin's emplacement - Early, possibly some Middle, Devonian age, although a small region in the park’s southwest corner is Late Devonian. Older Cambrian and Silurian rocks surround the park within the aforementioned basins, attributable to the tectonic and emplacement regime of the Katahdin pluton, of which less than half is within Baxter State Park.

    The Ascent Team
    Our "ascent team" included my son Will (left) and his friend Leo, both fit as a fiddle and seriously pumped to climb - as one can plainly see. The Hunt Trail is crossing Katahdin Stream on a bridge of logs. Massive boulders of Katahdin granite are everywhere. As the grade increases, the boulders will stack into a near-vertical wall.

    The cold October night created a temperature inversion in the valleys around Katahdin. Looking like a large lake off to the west, trapped cold air created a thick foggy blanket that quickly burned off in the sun. Still near freezing, we immediately began shedding layers as the pitch and our efforts increased.

    Temperature Inversion Fog

    Picturesque Katahdin Falls, at an elevation of about 1,600 feet, spills over a wall of Katahdin granite. The bedrock is homogeneously granitic on the Katahdin pluton, so the knickpoint didn't form on strata of varying lithologies with differing erosion-resistance typical of a sedimentary rock-dominated terrain. Instead, the falls is a consequence of the varying glacial landscape and mass-wasting that was rendered to the region after 12,000 years of erosion. At this elevation, the forest is predominantly red-black spruce and balsam fir that provides a veneer of aromatic and spongy, orange-brown needles everywhere.

    Katahdin Falls
    The calmness bequeathed here is in contrast to the arduous climb that awaits above.

    The boreal forests of Baxter State Park began to develop about 12,000 years ago with the regression of the Laurentide ice sheet. The land retained its tundra ecology for at least 1,000 years as the first human inhabitants left evidence of their presence. As the climate gradually warmed, it had a profound effect on the resident animal population. Northern forests of spruce and fir support relatively little herbaceous vegetation, offering little subsistence for gregarious herbivores like musk ox and caribou that gradually drifted northward out of the region.

    Today, 8,000 or so years later, the forests of northern Maine changed from boreal to spruce and fir-dominated. The regional soil is generally poorly to moderately drained over compressed glacial till or areas of shallow soil clinging to the bedrock. A great many of the forests have been harvested for logging, but Baxter is a "gem in the woods" - literally.

    Upon gaining altitude, the terrain began to unfold. It was even more clear that Katahdin is situated in an extensive forest of the Maine Wilderness. The stands and bands of bright-orange Sugar Maples in the valleys are growing on alluvially-enriched soils generated by huge glacial meltwater channels from the Pleistocene. As we progressed upslope, the soil-till-talus mix gave way to talus-dominated, and ultimately bedrock sprinkled with weather-fractured blocks of granite. The mosaic of hardwoods and softwoods is evident with the change in autumnal color.

    The mountains immediately off to the west of Katahdin have names such as Squaws Bosom, Tabletop, Barren, The Owl and the Brothers. Every one is cored with intrusive granite of the Katahdin pluton. That's not the case north of Katahdin where Traveler Mountain is composed of bluish-gray extrusive rhyolite, yet it's part of the same pluton, or better stated, volcanic complex - a hint at the co-magmatic regime of Katahdin. By the way, Traveler got its name from the early explorers that boated down the East Branch of the Penobscot River since the mountain seemed to travel with them.

    Macrolichens of New England
    A foliose (leafy) and a fruticose (shrubby) lichen - two of the main types - germinate on a hardwood branch. Exposed rocks, particularly at higher elevations, are covered with the third lichen-type - crustose (crusty).

    To the west, beyond the composite of summits of the Katahdin pluton and those of the Piscataquis belt, lies the aforementioned sedimentary, Salinic basin of the Connecticut Valley-Gaspe synclinorium. The extensional trough formed in the Middle Silurian within previously-accreted magmatic arcs of the Taconic orogeny (the Shelburne Falls and Bronson Hills arcs) that separated them. The sediments that accumulated within the trough were overlain by those derived from the foreland of the encroaching Acadian orogen. 

    The Migration of the Acadian Front
    Map of Maine showing sequential positions of the Acadian deformation front in its migration from the southeast to the northwest. The region of the Katahdin pluton is encircled. Note the time stamps. 
    Modified from Bradley and Tucker,2001. 

    With the convergence of the Avalon terrane in Late Silurian to Middle Devonian time upon Laurentia’s eastern margin and the trough, the Acadian front and foreland basin migrated northwestward across Maine, adjacent areas of New England, and New Brunswick and eastern Quebec of Canada. With the orogen's advance, it overrode and deformed the earlier Taconic-modified margin and inundated its migrating Acadian foreland basin with clastic successions of Devonian flysch and molasse and blanketed some of the deep-water Silurian sequences that accumulated within the synclinorium.

    The landscape we see today records these Silurian and Devonian sedimentary deposits and retains the barely perceptible, synclinal geomorphology of the extensional tectonic regime. But by what tectonic design did Katahdin and the Piscataquis volcanics emplace?

    View West from the below the Hunt Spur
    The bare granite cliffs to the right are on The Owl. Notice the rockslides on the slopes beyond. Heavy rains saturate the thin cover of soil on steep slopes that are poorly retained on the smooth granite. When they catastrophically fail, steep treeless scars record the event, never to reforest. Also, notice the enigmatic bands of "patterned growth" (Caldwell) or mortality patterns of the spruce and fir in front of the Owl to the far right. Except for elevation, topographical factors are not consistently related to the mortality. A budworm outbreak that reaches epidemic proportions about every 35 years has been implicated. Other hypotheses for the banding include host trees overtopped by hardwood canopies and factors relating to drainage and soil-type.


    Volcanic rocks within the Acadian orogen occur in two broad belts: a Coastal belt that erupted into the basement of the Avalon terrane and a second belt of Silurian-Devonian volcanic rocks – called the Piscataquis magmatic (or volcanic) belt within the foreland of New England (and the Tobique volcanic belt in Canada).

    Plutonic activity in this part of the orogen was produced by Acadian deformation and falls within a narrow range of the Emsian age of the Devonian (400-410 Ma.). The actual deformation front was south of the Katahdin pluton - placing it within the foreland basin, a location of emplacement that departs from the conventional tectonic norm.

    In addition, the ash-flows of Traveler rhyolite on Traveler Mountain to the north of Katahdin AND Katahdin itself are regarded as the volcanic and plutonic parts of the SAME igneous complex. In fact, the granite intrudes the rhyolite (on the north ridge of Wassataquoik Mountain and on the southern slope of South Traveler Mountain both to the north of Katahdin). The rhyolite-granite contact has been Zircon dated at 406.9 ± 0.4 Ma, which sets the maximum age for the granite. 

    The emplacement of the Katahdin pluton likely occurred at shallow depths because of the presence of the granophyric phase of granite and because the granite intruded its cover-carapace of rhyolite. Violent, successive eruptions at the surface spewed thick volcanic ash that flowed over the region preserved in the welded tuff of Traveler Mountain. If the carapace of Traveler rhyolite that once covered the likely caldera of Katahdin (formed when the volcano's magma chamber collapsed within itself), then the Katahdin volcanic complex would qualify as among the largest volcanic features known in the world (Hon, 1976). One can only imagine what this place was like during the Early Devonian!

    Geologic Map of the Katahdin Region
    Less than half of the Katahdin pluton is within Baxter State Park. Oval in outline and elongated in a NE-SW direction, it is roughly 40 X 22 miles and perhaps 3 miles thick. To the north the pluton is overlain by the Traveler rhyolite.
    Modified from Bradley and Tucker, 2001.

    Dating and geologic mapping have arrived at the conclusion that the upper parts of the Katahdin pluton are close to the roof of the magma chamber of the Katahdin granite and that the roof or carapace slopes north toward Traveler Mountain. We will see this in the phases of granite that crops out at various elevations on our climb. Where's the ash that we assume once covered Katahdin? It eroded away in the roughly 400 hundred million years since it blanketed the region, at a rate estimated at 20-100 feet per million years (Judson and Ritter, 1964). What's left of the ash comprises the rhyolite-tuff in the region of Traveler Mountain to Katahdin's north, all that's left of Katahdin's carapace.

    An Emsian-age transect (below) through the orogen in the Katahdin area shows the plutons emplaced into already-deformed Devonian rocks at a depth of 6.5 km. At this time, Katahdin is envisioned to entertain both "volcanism at the surface and plutonism at depth." (Bradley and Tucker, 2001). Emsian magmatism originated within and beneath the orogen BUT were extruded across the deformation front into the foreland. According to Bradley and Turner, "Although these younger plutons are commonly referred to as "Acadian," they postdated the documented cratonward advance of the deformation front and so cannot be linked to Acadian plate convergence."

    Nonpalinspastic Map of Maine
    Sequential positions of the Acadian deformation front are shown with dates as it migrated (arrow) across Maine (find borders of the state for orientation). In the Early Emsian (~407 Ma), the Katahdin pluton emplaced within the Acadian foreland. During this ~40 million year interval, the front is thought to have advanced some 240 km cratonward.
    Modified from Bradley and Tucker, 2001.

    The calc-alkaline, subduction-related granites likely possess a mantle component. The magmatism "cannot be solely a consequence of collision-induced thickening of continental crust" (Bradley and Tucker). One interpretation of the Katahdin-Traveler system is that mafic magma, generated deep within the mantle, ascended perhaps 20 miles from the surface beneath the crust (diagram below). Heat from the ponded magma partially melted the crust, generating a granitic magma. As the magma continued its buoyant ascent, it cooled and crystallized, accumulating gases within the upper chamber. The gas-rich magma escaped to the surface in a series of violent eruptions generating the
    successive ash flows of the Traveler rhyolite.

    Cross section through the Acadian Deformation Front during Early Emsian Time in the Katahdin Region
    From Bradley and Tucker, 2001.

    The volume of rhyolite that was produced is estimated to have been 80 cubic miles 
    compared to less than 1/10th of a cubic mile in the devastating 1980 eruption of Mount St. Helens. Typically, large extravasations of rhyolite lead to caldera formation with a rapid evacuation or pressure release within the magma chamber. It's likely that Katadin experienced some caldera formation, since some components of the Traveler rhyolite (Black Cat Member) demonstrate compaction foliation and faulting. Clearly though, the caldera-like geomorphology of Katahdin is the product of erosion following its exhumation.

    Unfortunately, I have no photos taken from within the Spur - a hundred feet or so of near-vertical, jointed granite. I admit that I was more concerned with safety than photography. However, I borrowed this photo from the web to illustrate my point.

    "What am I doing up here?" nicely sums up the Spur

    Leo and Will rejoice from the top of the Spur. Notice the Katahdin granite is now pinkish and blanketed by a black and yellow-iridescent lichen, largely Lecidea geographica. Eight distinct lichen habitats of almost 300 species have been found on Katahdin from its subalpine forests through the krummholz to the exposed alpine tundra at the summit. Lichens are sensitive to elevation, climate and air pollution. Bryophytes (liverworts and mosses) are also abundant - over 200 species.

    In the distance, the chain of post-Pleistocene lakes are within the Maine Wilderness Area. In the lowlands, orange Sugar Maples are sharply demarcated against evergreens that are thriving on nutrient-rich alluvium deposited during glacial melt.

    Atop the Spur
    Leo and Will rejoice at the top of the Spur.

    At about 3,850 feet, we're entering the Gateway - a ridge of boulder-strewn bedrock that leads to the flat plateau of the Tableland. Having negotiated the Spur we expected to have a glimpse of the summit but were surprised by the size of the Gateway. We were amused by descending climbers who exclaimed, "You're almost there!" - when in reality, there's another 4 miles to the penultimate summit of Katahdin! 

    We're clearly above the treeline. At this elevation, growing conditions have become increasingly severe with scarce nutrients, poorly drained, thin residual soils, wind, exposure and prolonged cold. Mineral soils have given way to organic soils. Most 
    herbaceous plants and tall trees can't tolerate these conditions. This is the sub-arctic krummholz or "crooked-wood" zone, dominated by tangled and stunted balsam fir, many in close stands that are almost impenetrable.  The krummholz transitions to the alpine zone once on the Tableland.

    At first glance, the plantscape appears uniform, but close observation shows a mosaic of 
    mosses, lichens and dwarf shrubs of fir, juniper and spruce. Microclimates and flora vary with the topography - expanses of bare bedrock, areas with thin soil and sheltered depressions out of the wind. You can tell the prevailing direction of the wind by the distorted shrubs that draw to the left.

    The Gateway to the Tableland
    The Gateway is a huge boulder-strewn ramp to the flats of the Tableland. That's Will, now wearing green, and Leo in black above him. The clouds are rolling in from the southeast (right) and dropping down into the cirque to the northwest. We experienced a sense of climbing into the "unknown." Further off to the right is the dangerous, steep and loose trail of Abol Slide, which also summits Katahdin from the west. 

    Katahdin's granite occurs in two phases. The variety that forms the core and most of the pluton is the granitic phase. Largely light gray and homogenous, its an equigranular (uniform), medium-grained granite. Compositionally, the granite is 33% quartz, 33% alkali feldspar, 25% plagioclase, 5-10% biotite and accessory minerals.

    As one ascends Katahdin, a gradual transition occurs from the light gray granitic phase at lower elevations, through mottled white and pink to salmon, and finally to brick red of the granophyric phase near the top of the pluton. The red comes from grains of hematite (iron oxide) contained within crystals of alkali feldspar. The color change is accompanied by higher percentages of fine-grained quartz and alkali feldspar that surround larger crystals with interlocking crystals. The geometric patterns one sees are typical of porphyritic igneous rocks and also contain small vugs (cavities).

    The coarser-grained granitic phase is thought to have cooled more slowly allowing for crystal growth, being closer to the interior of the magma chamber, than the granophyric phase, that cooled more rapidly being closer to the colder bordering rock. Water-rich gas bubbles near the roof of the chamber were trapped by the rapidly cooling granophyric phases.

    The Two Phases of Granite within the Katahdin Pluton - Granitic and Granophyric
    In these specimens photographed on Katahdin, one can readily identify white feldspars,
    black biotites and gray quartz.

    Parallel sets of through-going planar cracks or joints that develop in the granite fuel the mass wasting process that sends boulders downslope. It will eventually level Katahdin to a peneplain - the fate of all mountains in time. On the Tableland and scattered across Katadin's summit, the bedrock is broken into scattered boulders on the summit.

    The body of granite can also form joints from contractional cooling and from the strain induced by continent-deforming tectonic processes. Exfoliation or sheet joints are found on steep planar surfaces such as found on the walls of glacial cirques. They are formed more recently by unloading as the weight of the overburden is removed by erosion and the melting of glacial ice. Once formed, granite sheets can be further truncated by erosion as freeze-thaw cycles and gravity pry off the surface and fill the floor with talus debris.

    Transitioning from the Granitic to Granophyric Phase of the Katahdin Granite on the Gateway
    White blazes of paint and small cairns mark the trail. Notice the blanket of black and green lichens that cover the granite and its increasingly salmon color.

    Higher on the Gateway, Will forges ahead into the clouds that are streaming up from the cirque on the south face of Katahdin. Rainbow-colored curtains of water vapor shimmer in the wind. A gauntlet of lichen-speckled boulders are thrown everywhere in contrast to the tundral vegetation displaying fall colors. Incredibly beautiful. You want to stay, but the summit beckons. So does nightfall, as we carefully watch the time.

    Halfway up the Gateway
    Massive boulders litter the bedrock of the Gateway. "Almost on the plateau!"

    Off to the right are Mount Coe and South Brother. The lowlands to the left (west), 
    blanketed in colorful hardwoods, drape away from the Katahdin pluton onto till-covered Early Devonian, Ordovician and Silurian sedimentary rocks.

    Will clears the Spur onto the flat of the Tableland

    The southern region of the Katahdin massif is a broad, open, treeless, weather-exposed, gradually sloping plateau to the peaks that lie on the edge of the cliff-rimmed basins. Weathered blocks of bedrock were strewn everywhere, virtually coated with iridescent green-yellow lichen illuminated by the sun.

    The plants of this arctic zone at this altitude have evolved to tolerate the extreme environmental conditions. Grow low is the dominant survival tactic, but everything from shallow root systems to desiccation-resistant leaves contribute to their ability to thrive in this fragile habitat. Although alpine grasses exist, most herbaceous grass can't survive at this elevation and are mostly sedges. Lichens and mosses are also found in abundance. Climbing a high peak such as this is equivalent to traveling north to the arctic in terms of both the flora and fauna encountered. Many of the plants here are rare or endangered, and are protected by a cobble-lined trail to prevent trampling.

    View to the northwest from the Tableland
    The sign welcomes hikers to the Tableland.

    From the same location in the above photo on the Tableland, we're facing north. The peaks of Katahdin's summit appear to be nothing more than a long trek that ends on a plateau, which is what it is. But looks are deceiving in that the east face, which we can't yet see from here, is sculpted beyond anything imaginable. Also blocked from view, rhyolite-built, co-magmatic Traveler Mountain is 13 miles due north beyond Katahdin. We're nearing the top of the magma chamber that is Katahdin!

    From the Tableland, we're looking due north across a deep ravine that is the Katahdin Stream watershed. The flat-appearing, bare summit to the far right is Hamlin Peak, one of five that comprises Katahdin.

    Looking down from the Tableland to the Gateway, here's a last look at the tabular 
    landscape to the west. The "cloud factory" on Katahdin's south slope is still highly productive as the cool rising valley air meets the warmer air aloft. Our climb that began just above freezing is now a balmy 60 degrees.

    Several theories have been offered to explain the origin of the broad upland surface of the Tableland including erosional peneplanation and bevelling by glacio-peneplanation. The Tableland consists of resistant granophyric granite identical to that of Katahdin's summit. This resistant caprock in many ways is analagous to a sandstone overlying an erodable shale. Thus, the granophyre "holds up" or protects Katahdin. Once removed, rapid slope retreat occurs and decline into the hills and lowlands of the granitic phase around the pluton.


    From the same perspective looking due north (below), we're viewing Hamlin Peak (4,751 feet) to the right across the Northwest Plateau and Basin at the summit of Katahdin. Typical of glaciated terrain in the north, notice the glacial plucking on the south, leeward outcrop of granite. Viewed from the west, the plateau has a roche moutonnee or "sheep-back" configuration with a gently sloping, north face. Our view of Traveler Mountain is blocked by Hamlin peak. To the right are Fort Mountain and North Brother. Our destination of Baxter Peak is to the right (out of view) about 1.4 miles.

    We're near Thoreau Spring. Whether or not he actually reached this area is unknown. It is known from his journal that he never reached the summit of Katahdin, having been determined by bad weather. The Tableland is notorious for high winds and pelting rain and snow.

    In 1924, Governor Baxter lost his Republican party's nomination to Owen Brewster. While in office, Governor Brewster climbed and erected a plaque at the site of the spring as the first "sitting" governor to climb the edifice. Called Governor's Spring, he used photos of his climb to promote his proposal to convert the region to a national park. Baxter defeated the proposal and in 1933 purchased the first parcel of land of what would eventually become Baxter State Park. Of course the Governor's Spring plaque was replaced with one that reads Thoreau Spring - whether or not he was actually there. So the story goes. 

    After 5 hours of climbing, our efforts were rewarded with an unmatched view from the east side of Katahdin. Everything in sight is a compendium of a billion years of geological evolution - Rodinia's fragmentation, Paleozoic plate convergence, the closure of two oceans, Acadian deformation, Katahdin emplacement, the rifting apart of Pangaea, hundreds of millions of years of landscape erosion and exhumation, and finally, Pleistocene glaciation.

    Facing northeast from Baxter Peak, the glacial tarn of Chimney Pond lies 2,775 feet at the foot of the ice-carved, semi-circular cirque of South Basin - formed by erosion of an alpine glacier. With the cessation of glaciation, erosion has continued the process of excavation via mass-wasting and repetitive freeze-thaw cycles. Further out on the forest floor of glacial outwash and till, North and South Basins, also tarns, have been impounded by the Basin Ponds end moraine. In the middle distance, North and South Turner Mountains are separated by a glacial U-shaped valley. Rhyolite-composed Traveler Mountain, the co-magmatic partner of Katahdin, is in the clouds at the extreme left.

    Photographic documentation of our ascent to the summit of Katahdin! We're standing on weathered blocks of granite, although bedrock crops out just below the summit. On the far side of the sign is a 2,000 foot drop off to the valley below.

    Well done, Will!

    Leo and Will's turn in front of the lens!

    This photo says it all.

    This tablet on the summit of Mount Katahdin was placed on March 16,1932 to record the "gift and conveyance" of nine square miles of land to the State of Maine by former Governor Percival P. Baxter, made upon the express condition that the tract "forever be left in the natural wild state."

    Notice the salmon color of the granite. It is estimated that the roof of the pluton was only a few hundred feet above this spot. Also, observe the weather fractured cobbles, boulders and grus (coarse-grained sand and gravel resulting from the granular disintegration of the granite from mechanical and chemical weathering) that cover the summit. Even lichens contribute to the insidious dissintegration of the granite by secreting organic acids.

    The Knife Edge Trail (blue paint blazes) traverses the apex of a serrated arête that runs the mile or so between Baxter and Pamola Peaks. The north side of the ridge is formed by the glacial cirque of South Basin, while the south side, which likely was sculpted by the Laurentide ice sheet, doesn't bear the classical cirqued-features of alpine glaciation. The south side of the arête may be a greater victim of mass wasting and frost-shattering. Therefore, calling it an arête, which technically requires carving from alpine glaciers on both sides, may not be totally correct.

    That said, nothing detracts from the massivity of the ridge and the focus climbers must maintain while negotiating its exposed sections that are merely two feet wide in some areas and plummet some 2,000 feet in either direction. This is probably the most spectacular mountain trail in the East. High winds can be unpredictable and extremely menacing here. The Baxter State Park website posts the warning "Not for the faint of heart!"

    This photo faces east from Baxter and illustrates how the Knife Edge curves to meet Pamola Peak. If you click on the image to enlarge it, you'll see numerous hikers balancing their way across it.

    The Knife Edge

    From the same perch on Baxter Peak, we're looking south into the "cloud factory" of Katahdin's south face that we experienced earlier on the Gateway and the Tableland, which slopes off to the right. The Knife Edge begins off to the left. Notice the extent of weather-pulverized rock that litters the summit that completely blankets the bedrock.

    South-facing view from Baxter Peak

    The Knife Edge is rather blunted in this early section and covered by large boulders of Katahdin granite. At the far left in the sun, heavily-jointed, granophyric Katahdin bedrock is exposed at the top of South Basin's headwall and throughout most of the arête. Again, notice the climbers for scale. I counted 11 in the photo.

    The Knife Edge as it strikes east from Baxter Peak

    The Pleistocene epoch began in North America about 2.58 million years ago - traditionally referred to as the first of the Quaternary Period. Over this relatively short span of time geologically, the landscape of North America in Canada and the United States was dramatically altered by at least four phases of glaciation by an up to two-mile thick, slow-moving ice sheet called the Laurentide. Driven by vacillations in the climate, a multitude of glacial advances and regressions (glacial and interglacial episodes) occurred, the most recent of which is the Wisconsinan that extended to about 38 degrees latitude.

    Extent of Pleistocene glaciation at 18,000 years ago.
    Note the depth of the continental ice sheet in meters. Katahdin is at the red dot.
    Modified from A. McIntyre, CLIMAP Project, Lamont-Doherty Earth Observatory, 1981.

    Following Katahdin's emplacement in the Early Devonian, hundreds of millions of years of erosion worked to remove nearly two miles of overburden that buried the pluton. Looking back about 10 million years, we would likely see that the general features of the landscape in Baxter State Park were likely already fashioned. Once exhumed, Pleistocene glaciers began to sculpt Katahdin's modern landscape out of its granite.

    The Laurentide ice sheet flowed southeast across Maine and terminated at Georges Bank (a submerged area of the sea floor between Cape Cod and Nova Scotia) at a time when the level of the seas was 300 feet below present during glacial maximum. The oceans reached their modern level about 3,000 years ago and of course are on the rise - this being an inetrglacial epoch of warming called the Holocene - the most recent time frame of the Quaternary.

    Enough water was held in continental ice sheets during the Pleistocene to lower sea level worldwide by about 150 meters. When deglaciation and the ice age finally ended about 12,000 years ago, the ice sheet left the landscape of Katahdin and the surrounding lowlands with a distinctive array of erosional and depositional landforms in what is a textbook study in glaciomorphology. Few places in the northeastern United states offer a chance to see these features in such an unspoiled setting. Some 400 million years of surface erosion and post-glacial isostatic rebound have allowed the landscape to assume its present attitude almost a mile above sea level. 

    Sandy Stream Pond and Katahdin
    Sandy Stream Pond is one of the best places to see moose at sunrise or sunset. In the distance, Katahdin’s four cirques and five summits are dusted in late October snow. The low, elongate ridge beyond the treeline is the Basin Pond moraine that dams the Basin Ponds.
    Panorama contributed by resident Mainer Donny Doyle (

    North view of the Basin Ponds and the Basin Ponds moraine
    The Google Earth vertical exaggeration is greatly increased in order to visualize the Basin Ponds moraine that impounds three tarns at the foot of Great and South basins.

    Perhaps the most puzzling question concerning Katahdin’s glacial history was whether there was cirque glaciation on Katahdin following the retreat of the continental ice sheet of late Wisconsinan time or perhaps even whether alpine glaciation preceded the arrival of the ice sheet. A second question is whether Katahdin was a nunatak (an Inuit word) with its summit remaining isolated from glaciation.

    Glacial erratics found on Katahdin in addition to polished bedrock and striations indicate that Katahdin was in fact once covered by the last advance of the Laurentide ice sheet during Late Wisconsinan glaciation between about 25,000 and 12,-13,000 years ago (Davis, 1989). That disproves the hypothesis that Katahdin remained a nunatak during continental glacial advance (at least during the late Wisconsinan glacial maximum). On the other hand, arguements against the nunatak explain why the serrate topography such as the Kinfe Edge appears so fresh. The controversy that remains is whether the alpine glaciers persisted in the cirques after the ice sheet retreated to the north.

    I photographed this quartz-veined metamorphic rock high on the slopes of the Hunt Trail of west Katahdin. This small erratic is a confirmation of the glaciers that once covered at least a portion of Katahdin.

    In the past, many (including Caldwell, 1959) felt the cirques and arêtes were too fresh to have been ice sheet overridden and therefore shaped by alpine glaciers. More recently, it has been suggested that the continental ice sheet covered Katahdin but post-glacial mass wasting controlled by vertical jointing of the bedrock shaped the cirques and arêtes (Davis).

    Two scenarios are being entertained today. Caldwell envisions a "two-glacier" history - ice sheet followed by alpine glaciers. He interpreted the Basin Ponds moraine to be a medial moraine between alpine glaciers flowing from the east-side cirques and a tongue of the ice sheet flowing between Katahdin and the Turner Mountains to the east. Davis, on the other hand, hypothesized the continental ice sheet was the final glacial activity on Katahdin and interpreted the Basin Ponds moraine to be a recessional-lateral moraine of the waning ice sheet between Katahdin and the Turner Mountains. Clearly, the Basin Ponds moraine is the most controversial glacial feature in Baxter State Park.

    As we descended from Baxter Peak across the Tableland, the Saddle Trail can be seen below winding along on the low-lying, flat-topped ridge called the Saddle. The Saddle Trail traces the rim of the Great Basin before abruptly heading down the cirque on a precariously steep and loose rock slide from an avalanche that occurred during the winter of 1898-1899. Avalanche scars are common on Katahdin's steep slopes such as the Y-shaped one in the photo. Rockfalls are common as well on the cirque walls, weakened by joints and freeze-thaw action. 

    The Saddle
    Coming off the rubble-covered Tableland from Baxter Peak, the Saddle Trail dips into the Saddle.

    The surface leading to the Saddle is literally covered with weather-pulverized cobbles of granite with larger boulders peppered here and there.

    Weathered and frost-shattered granite literally painted with lichen on the Saddle

    Bright yellow-green and black lichens on the red granophyric phase of Katahdin granite were a feast for the eyes.

    We're looking back at Baxter Peak from the beginning of the Saddle, as we entered the densely packed and stunted trees of the krummholz zone. There are almost 50 people celebrating their ascent on the summit of Baxter, but you'd never know it from here. One group opened a bottle of champagne to toast their accomplishment.

    Glancing back at Baxter Peak, once we cometh, from within the krummholz

    The Saddle Trail strikes a rock-hopping path through the krummholz on large boulders of weathered granite. That's Will in the green shirt picking his way down. The landscape pitches to the right in the direction of the cirques.

    Krummholz zone of the Saddle

    The first portion of the Saddle Trail is appropriately called the Slide on the start of Great Basin's headwall. The going is slow on thin, steep ledges and loose slide material. Cathedral Ridge and Trail are in the middle distance - an arête that separates Great Basin from South Basin. The three knobs on the trail are the "cathedrals" formed by the erosion of porphyritic granite that has been sectioned by vertical joints. Triangular-shaped Chimney Pond is at the base of South Basin at the foot of the headwall that rises to Pamola Peak in the clouds. As one progresses downslope, the red granophyric phase of granite gradually transitions back to the light gray granitic phase, the reverse of what we saw on our west side ascent.

    By way of review, every feature in immediate view is composed of intrusive, Devonian-age Katahdin granite with the exception of the more easily eroded sedimentary rocks of the lowlands. The volcano's carapace of extrusive tuff-rhyolite has been eroded away in the process of its exhumation with the exception of Traveler Mountain.

    Surprisingly, the majority of the granites in Maine don't form mountains. The multi-phasic structure of the Katahdin granite - the granophyric phase in particular - is responsible for building the high mountain edifice, or better stated,  preventing its erosion. Finally, glaciers of the Pleistocene are responsible for the extreme topography, and its erosional and depositional features and landforms.

    For another perspective of South Basin, here's a Google Earth view from the middle of the Saddle Trail, which we descended in the above photo. The caldera-like morphology of Katahdin is a consequence of glacial erosion, mass wasting and freeze-thaw action, although some calderic collapse was a likely occurence during Katahdin's post-emplacement history. The U-shaped bowl of South Basin is framed by the arêtes of Keep Ridge on the left and Cathedral Ridge on the right - created by the action of alpine glaciers excavating both sides of the ridges. At the top of the headwall, the Knife Edge runs from Pamola to Baxter Peak.

    In the distance (below), Upper and Lower Basin Ponds are dammed by the Basin Ponds moraine just beyond them - the puzzling feature that we discussed. The moraine stretches nearly three miles and has as much as 50 feet of relief. Its largely consists of granite in all sizes, some up to 20 feet  across. It's noteworthy that Davis (mentioned earlier) found that 10-44% of its rocks were non-granitic - in keeping with his only an ice-sheet-conclusion. Davis further pointed out that the ridge of the moraine is convex westward - a curvature opposite to what one would expect from alpine glaciers that might have originated from the west on Katahdin. What's your interpretation? No Biblical Flood theories please.

    The ephemeral Dry Pond in the foreground is water-filled. Beyond, Whidden and Sandy Stream Ponds are almost hidden in the forest before the slopes of South Turner Mountain.

    Subglacial sediment transport as debris-rich ice were deposited as meltout till, but other depositional landforms exist as well in Baxter State Park. While a large drumlin-field exists in southern Maine, the Katahdin esker system consists of a sinuous, branching network of poorly-sorted sand, gravel and boulders that stretches 150 km from its source near the entrance to Baxter State Park just south of Katahdin to its terminus at Pineo Ridge near the Maine coast. These glacio-depositional landforms were left in the wake of the receding ice sheet.

    Eskers are constructed by subglacial streams and rivers flowing within ice-walled tunnels along the glacier bed. Their resemblance to long-abandoned railway embankments led Maine old timers to humorously refer to them as "Indian railroads." In fact, some rural roads in the area are built along the crest of an esker.      

    The Basin Ponds, Dry Pond and the Basin Ponds moraine
    The setting sun on the opposite side of Katahdin is casting long shadows across the valley.

    Perched on a thin ledge of the Saddle Trail, the view was unmatched. That's Katahdin Lake in the middle distance. The Canadian border between eastern Maine and the province of New Brunswick lies 55 miles due east, and Nova Scotia and the Bay of Fundy is another 160 miles.

    For the record, the Bay of Fundy lies in a rift valley called the Fundy Basin. The rift began to form when Pangaea began to break up in the Late Triassic. The formation of the Atlantic Ocean placed Katahdin and the entire Appalachian Mountain range within reach of the sea along North America's east coast.

    View from the Saddle Trail of the glacial valley at the merging of the foot of the cirques

    Vertical-jointed granite on the knobs of Cathedral Trail stand out in profile. Beyond, Pamola has briefly emerged from the clouds. The notch to the right of the peak is the ridge-crest manifestation of the Chimney, a northwest-trending fault zone of highly fractured rocks that continues to the foot of the cirque as a steep, narrow gully or couloir. The Chimney is a popular challenge for technical climbers heading to the Knife Edge.

    Pamola Peak and the Cathedral Ridge in profile from Saddle Trail

    From the Ranger Cabin at Chimney Pond, the impressive semi-circular headwall of South Basin dominates the frame. The sun was very low on the horizon on the far side of Katahdin. You can make out curtains of granite that are exfoliating from the headwall.

    Eight or nine recognizable cirques surround Katahdin with the exception of its south flank. The three largest are on the east side of the mountain. Why are the east-facing cirques larger than the others? One explanation is that prevailing northwest winds blow snow to the largely sun-sheltered east-side cirques. A similar prevailing climate during the Pleistocene would have encouraged the cirque-size disparity.

    The sheer headwall of South Basin

    From the water-filled Dry Pond seen from above, we're looking back at the base of the Cathedral and Great Basin beyond. Wet Pond is an ephemeral tarn that is subject to the whim of precipitation from the watershed of South Basin. Outwash deposits from meltwater streams blanket the region as do erratics of all shapes and sizes.

    A not-so-dry Dry Pond

    Pamola, the bad-tempered, winged deity of Katahdin, was good to us. Our west-to-east traverse was a resounding success and an invigorating experience in terms of the geology and the fun we had. Our 10-mile expedition took 11 hours to complete. The only problem was that our car was over 20 miles away on the opposite side of the mountain. Having arrived in the valley and forest wilderness after dark, we more fully appreciated why the gate attendant asked if everyone was carrying a flashlight. Fortunately for us, it was a brilliant full moon, and we didn't even need one.

    Our plan to hitch to our car was totally unsuccessful in that virtually none were leaving the Roaring Brook campground. Fortuitously, a conversation we struck up with a Search and Rescue Ranger on the trail resulted in him radioing ahead to the Park Ranger, unbeknownst to us, who picked us up on the forest road and gave us a lift back to our car.

    That's Leo and Will in the back of the Ranger's pickup. Thank you Baxter Park Rangers and Governor Percival Baxter for making it all happen. What a great day!

    "What you get by achieving your goals is not as important as what you become by achieving your goals."
    Henry David Thoreau
    A Guide to the Geology of Baxter State Park and Katahdin by Douglas W. Rankin and Dabney (Dee) W. Caldwell, Maine Geological Society, 2010.
    Baxter State Park and Mount Katahdin - Trails Illustrated Topographic Map, National Geographic, 2011.
    Emsian Synorogenic Paleography of the Maine Appalachians by Dwight Bradley and Robert Tucker, The Journal of Geology online, 2001.
    Foreland-forearc Collisional Granitoid and Mafic Magmatism Caused by Lower Plate Lithospheric Slab Breakoff: The Acadian of Maine, and Other Orogens by A. Schoonmaker et al, Geological Society of America, 2005.
    Guidebook for Field Trips in North-Central Maine, 105th Annual NEIG Conference, 2013.
    The Geology of Baxter State Park and Katahdin, Bulletin 43, Plate 1 - Bedrock Geology and Plate 2 - Surficial Geology, 2010.
    Roadside Geology of Maine by D.W. Caldwell, 1998.

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    In March, I escaped from the frigid grip of the Polar Vortex that enveloped New England and found climatic, cultural and culinary refuge in Paris and London. Not expecting to encounter any geological discoveries worthy of a post, I found precisely the opposite. Herein is the first of two posts on the Geological Legacies of the Paris Basin, and later, a few worthy geo-gems I found in London. 

    The Romans called their settlement on the south bank of the Seine River Lutetia Parisiorum or Lutetia of the Parisi, after the Gallic people who settled in the area in the third century BC. Lutetia (Lutece in French) is thought to have been derived from a Celtic root-word luteuo- meaning "marsh" or "swamp." Lutum is also the Latin word for "mud."  

    The settlement also lent its name to the Lutetian Age of the Eocene Epoch that occurred 41.3 to 47.8 million years ago. It was a time when the Paris Basin was invaded by a shallow, warm tropical sea from the north of Europe, one of many marine cycles that have flooded the region. It was also a time of marine sedimentation and the evolution of a carbonate platform, when Lutetian gypsums and limestones formed. Its rocks would eventually help to construct the buildings, monuments and churches of the city of Paris. 

    The official international reference point (GSSP) for the Lutetian is located in the limestone strata of the quarries below the streets of Paris at a water-well that bears the name Bain de pieds des carriers or the Quarrymen's Footbath. The descent to the footbath cuts through the Lower Lutetian limestone allowing the age's precise identification. We'll visit the footbath on post Part II, when we investigate the subterranean catacombs of Paris.

    Perched high above Paris on "La Butte" of Montmartre stands a windmill called le Moulin de la Galette or the Mill of Galette. More precisely a cluster of windmills than any one in particular, it was built in 1717. The name is derived from a “galette” - a flat crusty tart baked by the Debray family, the mill’s nineteenth century owners and millers. Along with
    le Moulin de Radet down the street and Moulin a Poivre nearby, they were the last of perhaps thirty (the numbers vary in the literature) that once dominated the heights of Montmartre, a once pastoral village dotted with vineyards on the northern outskirts of Paris and now a heavily touristed, upscale residential district of the city.

    The windmill was also known as the Blute-Fin - from the French verb “bluter” which means to sift flour. In addition to grinding corn and grains, and crushing grapes and flowers, many of the mills crushed gypsum into a fine powder for the making of plaster of Paris.

    The Mill of Montmartre
    In the first quarter of the nineteenth century, bucolic Montmartre
    was a picturesque Paris suburb of windmills and vineyards.
    Georges Michel, oil on canvas, ca. 1820

    Moulin de la Galette and Moulin de Radet on Rue Lepic near the end of the nineteenth century
    Public Domain

    According to French history, four Debray family men were involved in defending Montmartre and Paris against the invading Cossacks in 1814. Three were killed with one being quartered and nailed to the blades of the windmill. So the legend goes. The surviving fourth transformed the windmill into the Blute-Fin. The family is buried in the butte's small cemetery with small red windmills marking their graves, a fitting memorial to their nationalistic pride. 

    As we shall see, the Impressionist artists turned their attention to the windmills of Montmartre, joining the tradition of a cadre of great masters in celebrating an iconic image of Bohemian Paris. Today, the windmill stands as a French national monument with a great story to tell - one where history, politics, philosophy, art and even geology come together.

    Moulin de Radet, a few doors down Rue Lepic from Moulin de la Galette

    The country village of Montmartre arose on a 420-foot butte above Paris, which served to isolate it from Paris - for a time. Its core contained extensive deposits of layered gypsum - "gypse" in French - derived during the Lutetian Age that played into the history of the region. The word gypsum is a contraction of two Greek words, "ge" for earth and "epsun" meaning to concoct. The soft mineral was sought after throughout Europe and across the Atlantic in the 18th and 19th centuries. For it was gypsum that was processed into plaster of Paris. 

    Entrance to a quarry at the foot of Montmartre in 1832
    Artist unknown
    Photograph of visitors to a Montmartre quarry
    The "room and pillar" mining method (piliers tournes), by excavating the deposits into a cathedral-like vault, reinforced the ceiling with a supportive buttress. Given gypsum's fragility, due to its water-solubility and mechanically weak nature, street and house collapses were common. A famous accident occurred in 1778 where horses, wagons and people were engulfed. Regulations and edicts followed with the establishment of the position of Inspector of the Quarries by King Louis XVI, who's responsibility was to map and reinforce the quarries. Note the stratification of the gypsum, marl and sand in the quarry walls, referred to as "masses" in the geological French literature. The average mass of gypsum was about 5 to 20 meters thick. Limestone is buried below the gypsum and is prominent in Paris.
    The gypsum quarries of Montmartre on the Right Bank (and as we shall see later, the limestone quarries of the Left Bank) literally riddle the depths of Paris. Since the time of the Romans, Montmartre has been heavily quarried. Mechanically weak and highly soluble, gypsum offers no resistance to cave-ins and is a great impediment to construction. Even over a century after the mines closed, many areas remained unbuildable.

    Cathedral-like vault in a Montmartre gypsum quarry with wooden shorings to prevent collapse

    When approaching Paris from a distance or seen from the Eiffel Tower in the photo below, one of the most conspicuous buildings is the gleaming travertine of the Basilica of Sacre Cour, dedicated to the Sacred Heart of Jesus on the penultimate summit of Montmartre. Built between 1875 and 1914, the absence of large surrounding structures isn't because developers desired to maintain the butte's rustic ambiance. It's because the undermined, gypsum terrain is unsuitable to withstand the weight. To overcome the obstacle, the travertine of Sacre Cour required specially deep foundations during its construction to secure it from collapse. An intergral part of Paris today, it takes some imagination to envision the butte of Montmartre only 175 years ago as a hilltop village.

    Seen from the top of the Eiffel Tower, the Basilique du Sacre-Cour towers over the Butte Montmartre. By the way, Montmartre is thought to have derived its name either from the Romans, who called it Mont de Mars (in French), or the early Christians, who called it Mont des Martyrs for Saint Denis who was arrested and beheaded at the top of the hill in the third century. On the site before the construction of the basilica, the Abbey of Montmartre built in 1113 used the early windmills of Montmartre to crush grapes for winemaking that were grown in the vineyards that covered the hill in the 16th century. 

    After removal from the quarries, gypsum was heated in kilns at 300º F to drive off water and brought up the road on wagons pulled by donkeys or oxen to the mills for grinding. Romantic and colorful images of the early mining and milling days of Montmartre were created by a cadre of Impressionist artists that gravitated to the area not only to paint but to take up residence. They document the pastoral nature of Montmartre, its windmills on the heights and the quarries below.

    Early Windmills and Montmartre Quarry
    Artist and source unknown

    Montmartre the Quarry and Windmills
    Vincent van Gogh, oil on canvas, 1886 

    After milling, the calcined ground gypsum was bagged and sent downhill by wagon on its way to global markets via the River Seine. At the foot of Montmartre, it passed through the Barriere Blanche or White Barrier, a gate built for the collection of taxes for goods such as plaster coming into the city of Paris and named for the white powder that spilled from the wagons on the facades of buildings and the roadway.

    Bagged plaster loaded onto wagons
    Museum of Fine Arts in Bordeaux

    Later, the gate became the Place Blanche or White Plaza. Even the Paris Metro train station is called Blanche. Francophiles will recognize the plaza as the location of the Moulin de la Galette-inspired Moulin Rouge or Red Mill. The faux-mill was a fashionable cabaret that opened at the foot of the Montmartre hill in the red-light district in the late nineteenth century and home of the anatomy-revealing can-can dance. And nearby at the top of the Rue Lepic on Montmartre, the historic Moulin de la Galette is still open for business as a restaurant.

    At the Moulin Rouge, the Dance
    Henri de Toulouse-Latrec, oil on canvas, 1880 

    The impact of geology on the evolution of Parisian history acted in both subtle and obvious ways - the butte location of Montmartre (which has also served as a strategic military location), its gypsum-grinding windmills, and the establishment of Montmartre's artistic heritage based on its geographic and political location and isolation.     

    When water is re-added to heat-calcined gypsum, it forms a hard setting paste - a calcium sulphate hemi-hydrate or plaster of Paris. Amongst its many desirable properties, the compound is a non-combustible, natural fire retardant and insulator that absorbs heat and only releases water vapor in a fire. It was not only used on building facades but as a stone mortar by the Romans in the first century. It was also a sculpting material and used for decorative architectural purposes on tiles and frescoes dating back as far as the ancient Egyptians and Mesopotamian cultures.

    Paris escaped devastating urban fires since the late Middle Ages, in part because of plaster on interior and exterior walls. One year after the Great Fire of London in 1666, French King Louis XIV decreed that timber-framed structures were to be covered with plaster. That put Montmartre and its gypsum deposits on the map. But it was Louis-Napoleon Bonaparte, later to become Emperor Napoleon III and the nephew of Napoleon Bonaparte, that took the city of Paris and Montmartre in a completely different direction, a path that would end gypsum mining and radically change the urban landscape.


    In this 1820 view of the butte of Montmartre, urbanization has already begun, yet the gypsum quarries, both open and underground, were still present. Off to the left you can make out two windmills. Mining would change under the reign of Napoleon III.

    In 1848, Louis-Napoleon arrived in Paris from London at forty years of age. After a family exile of thirty-three years, he brought back his architectural experience of Europe's grand cities and envisioned the same for Paris. After becoming the first president of France in 1853, Napoleon and his appointed Prefect of the Seine, Georges-Eugene Haussmann, initiated a seventeen year plan of radical demolition and extensive reconstruction of the city of Paris. Napoleon's quest to build a modern European French capitol had begun, and its buildings and monuments would rise out of the limestone buried beneath the city.

    Percement de l'avenue de l'Opera in Paris awaits demolition
    Photograph by Charles Marville, Napoleon III's official photographer of Paris beginning in 1862 to document the "Haussmannization" of Paris. Marville excelled at architectural photographs and poetic urban views, capturing everything from Paris's oldest quarters, narrow streets, buildings, monuments and gardens to lampposts and urinals. Marville captured the transition from the Old Paris to the New. The emptiness of the streets is very misleading, because in all likelihood, it was filled with people and vehicles. The long exposure times necessary to capture the image on a negative failed to preserve any transient passersby.

    The "Old" Paris of crowded, dangerous, filthy, disease-infested, narrow labyrinthine streets was razed and transformed into a modern "New" Paris of broadly radiating boulevards, elegant parks, public buildings, private palaces, apartment complexes, ornate fountains, decorated bridges, reliable water, sewer systems, facade-standardized buildings, railroads, gas street lamps and even public urinals for men - essentially the modern Paris of today.  

    "Paris is an immense workshop of putrefaction, where misery, pestilence
    and sickness work in concert, where sunlight and air rarely penetrate.
    Paris is a terrible place where plants shrivel and perish, and where,
    of seven small infants, four die during the course of the year."
    Considerant, French social reformer, 1845

    Paris Street, Rainy Day
    This 1877 oil of Gustave Caillebotte is a snapshot of Haussmann's elegantly rebuilt Paris with its exaggerated, plunging perspective and flat colors. Notice the broad avenues lined by monumental canyons of facade-alike buildings topped by mansard roofs and anonymous, well-to-do (notice the pearl earring) Parisians strolling along in the rain (called flaneur, a stroller with rich connotations). Caillebotte was a member of the upper class and an Impressionist, although his short brushstrokes are barely visible. About the "new" Paris, historians believe that an additional motivation for the new street design was to facilitate the movement of troops and make the city revolution-proof. What renovation surely did was to displace the working class to outlying villages such as Montmartre, an event that, in part, facilitated the advancement of impressionistic art on the Parisian scene. Although the razing of Paris in a sense brought the impressionists together in Montmartre, they were detached by the social upheaval and physical destruction of Paris. Napoleon eventually fired Haussmann in 1870, who was criticized for the immense cost of the project.

    Reminiscent of Greenwich Village, a former bohemian haven and now upper-class neighborhood in New York City, Montmartre's autonomy as a country village has survived, in part, by virtue of its isolated geography having been a train ride or one hour walk from center Paris up the heights, as well as having escaped Haussmann's radical renovation.

    Montmartre was outside the Mur des Fermiers generaux (the Wall of the Farmers-General), a 28 km long, physical and fiscal barrier that surrounded Paris built by King Louis XVI between 1784 and 1791. Rather than acting as a defensive barrier against invasion, unpopular entry tolls were extracted and duties were levied on goods entering the city (called "octroi") at various point along the wall. The wall contained 47 gates and 16 tollhouses, many with architectural merit. Interestingly, some portions of the wall still exist as an elevated roadway and four tollhouses remain. We'll enter one in my Post II at the Barriere d'Enfer on the Left Bank and descend into the limestone quarries beneath the streets of Paris. 

    Map of Paris (pink) and environs (tan) in 1841, sliced in two by the west flowing River Seine. 
    The larger, outer 33 km enclosure (red) is the defensive Thiers Wall constructed between 1841 and 1844, whereas the inner enclosure is the Wall of the Farmers-General constructed between 1784 and 1791. The two arrows mark the locations of gypsum quarries in the villages of Montmartre and Bellville outside the Farmers-General wall. The majority of the toll barriers were destroyed during Napoleon III's expansion of Paris in 1860. Notice the meandering course of the river within the sedimentary basin of Paris (Bassin de Paris).

    Unable or unwilling to pay the entry taxes and displaced by Haussmann's city-wide renovation, thousands of the less well-healed working class of laborers, farmers, seamstresses, milliners, students and artists departed from Paris. Outside the customs barriers and the taxman's reach, Montmartre's quiet streets and low rents made it a melting pot for free-thinking bohemians, dissident politicians and the young avant-garde.

    As for the fourteen windmills on the hill, they had less to grind. The gypsum quarries closed in 1860, the same year that Montmartre was annexed to Paris with the destruction of its walled enclosure. Today, Montmartre is within the 18th arrondissement - Paris's clockwise spiral of municipal districts - yet still retains its medieval, narrow maze of streets in contrast to the "new" Paris in the flats below the butte.

    Looking down a steep Montmartre street from Rue Lepic toward the flat terrain of Paris, the Moulin de Radet is directly behind. The gold dome in the distance is L'Hotel National des Invalides across the Seine. The complex was a hospital and retirement home for disabled war veterans built by King Louis XIV in 1670. Today, it's a military museum and burial site for Napoleon Bonaparte. Out of view, the Eiffel Tower is off to the right. 

    As for the Moulin de la Galette, it was repurposed by the Debray family into a "guinguette," after a sour local white wine called "ginguet". Guinguettes were colorful, outdoor, raucous establishments for eating, drinking, laughing and enjoying life and nightlife. It was where bourgeois (middle class) patrons from Paris could rub elbows with prostitutes. It was where dancing was allowed where you could touch your partner!

    Furthermore, it had an even greater impact as a place where Paris's displaced intellectuals, artists, writers, poets, musicians, sculptors and architects gathered. Impressionist paintings of carefree Parisians enjoying Montmartre - by artists such as Renoir, van Gogh, Degas, Picasso, Modigliani, Utrillo, Toulouse-Lautrec and others - documented the evolution of the two cities - and even their geological histories! Let's return to the quarries of Paris.

    Bal (dance) du Moulin de la Galette
    Renoir depicted cheerful and carefree, middle-class Parisians wearing their Sunday best, enjoying life in the guinguette of Moulin de la Gallette. With music played by a ten-man band, not only modest quadrilles were danced where only hand-touching was allowed, but patrons danced the Viennese waltz with real bodily contact. He was the first artist to transfer a scene of everyday life to a large canvas with brushstrokes that could be seen in the style of the impressionists. Classical artists before this time painted only biblical, mythological and heroic events of times gone by.
    Pierre-Auguste Renoir, oil on canvas, 1876.

    Sedimentary deposits of gypsum were generally located in the north and northeast quarters of Paris, mainly in the neighborhoods of Montmartre, Buttes-Chaumont, Charonne and Menilmontant. Gypsum is present in South Paris across the river but in thinner deposits. On the map (below) of the "Old Quarries of Paris," the two main quarries of gypsum (green shaded) are identified by arrows in the villages of Montmartre on the left and Belleville on the right, both on the Right Bank (north side) of the River Seine.


    Stratigraphic Map of Paris
    In 1811, Georges Cuvier's (early nineteenth century founder of vertebrate paleontology) and Alexandre Brongniart's (scientist and mining engineer) stratigraphic portrayal of the Paris Basin in the region of Paris. With colors, they identified layers of limestone (craie and calcaire), gypsum (gypse) and marine marls (marnes). Their discoveries proved that the stratal formations in the Paris Basin had been deposited in alternating fresh and saltwater conditions, implying the existence of inland seas at various times in the remote history of the region. Although Cuvier's concepts of evolution were catastrophic with new species forming after Noah's Flood, his concepts of biostratigraphy were ground breaking (pun intended).

    The Lutetian-age gypsum that was quarried in Paris's northern tier was called ludium gypsum in strata separate and above that of limestone in the southern tier called lutetian limestone. Before the initiation of limestone formation, 50 million years ago, deformation elevated the southern portion of the Paris Basin. The sea repeatedly transgressed and regressed over the region forming carbonate banks. Once elevated, a crustal fold confined sea water to lagunas that formed evaporites of gypsum in layers. The geological fold - called the Ypresian fold - acted as a dam on the upper plateau south of Paris. The contemporary result was high concentrations of gypsum in the subsurface and limestone to the south near the surface (20 to 30 m).

    In French, the four masses of gypsum found in the northern tier of Paris
    Gypsum has a high solubility, but its presence was protected from dissolution by a thick overburden of clay. Each of the four deposits received a colorful name by the quarrymen: les fleurs (the flowers), le gros cul (the big ass), les foies de cochon (pig livers) and les pots a beure (butter pot) or les crottes d'anes (donkey droppings).
    From exploration.urban,free,fr

    Across the River Seine from Montmartre that slices Paris into its two famous banks, the Left Bank was open-pit mined for its "coarse" limestone (calcaire grossiersince Gallo-Roman times. In the 17th and 18th centuries, mining went underground. That practice honeycombed the depths of Paris even more than Montmartre with miles of subterranean (souterraines) quarries. As with gypsum, the deposits of limestone and their quarries have affected the historical, political, cultural and creative evolution of the city of Paris. What is the Paris Basin, and how did it form?

    Ancient Gypsum and Limestone Quarries of Paris in 1908
    The River Seine follows the trough of the Paris Basin to the Atlantic Ocean. In so doing, it divides Paris into an “elegant” Right Bank (Rive Droite) and a “bohemian” Left Bank (Rive Gauche). Green shading on the Right Bank indicates the underground mines of "gypse" or gypsum clustered at Montmartre (left arrow) and around the villages of Belleville and La Villette (right arrow). The red shading, largely on the Left Bank, indicates the mining of "calcaire grossier" or coarse limestone.

    Modified from Wikipedia.

    More than just the immediate lowland around its namesake, the Paris Basin covers a vast portion of northern France – over 140,000 square kilometers - and measures 500 by 300 km. The basin extends northwestward below the English Channel into the London Basin and connects to the Belgium Basin to the north - summarily referred to as the Anglo-Paris Basin.

    Simplified Geologic Map of Europe Showing the Main Orogenic Systems and Sedimentary Basins
    From Geology of Europe by Franz Neubauer

    The 776 km Seine River and its tributaries drain the basin and slice Paris into its two famous banks – Left and Right for south and north. The basin recharges along its eastern border and discharges to the English Channel’s seafloor at Le Havre, Normandy.

    Geologically, the Paris Basin is an intracratonic (intraplate) sedimentary trough of flat valleys and low plateaus built on a collapsed Variscan collisional belt. The depocenter resides on an extended continental shelf (epicontinental) of the Eurasian plate that has been periodically invaded by marine high seas. It's built on a Cadomian-Variscan crystalline foundation surrounded by crystalline highs of late Paleozoic age and came into existence during a period of rifting in Permo-Triassic times.

    Topographic Satellite Image of France
    The upper central portion of the satellite photo is dominated by the Paris Basin and the Seine River and its tributaries. Paris is located at the red dot. In France, four main rivers drain west to the Atlantic, the Seine,the Loire and the Garonne, and one south to the Mediterranean, the Rhone.
    NASA Visible Earth Image Courtesy of Shuttle Radar Topography Mission Team

    The basin's tectono-sedimentary history is complex with several aspects that are poorly understood and strongly debated. For clarity (I hope), I divided the events into stages: (1) Acquisition of Cadomian basement; (2) Avalonia-type terranes accrete to Laurentia; (3) Cadomia-type terranes accrete to Laurussia; (4) Variscan orogeny forms a Gondwana Europe within Pangaea; (5) Post-Variscan extension creates epicontinental depocenters; (6) Pangaea rifts apart sending peri-Gondwanan terranes across the Atlantic; (7) Global high seas repeatedly flood epicontinental Europe; (8) Alpine Orogeny shapes and confines the basins.

    (1) Acquisition of Cadomian basement rocks
    The break-up of the supercontinent of Rodinia in the latest Proterozoic to Early Cambrian (ca. 0.75 Ga) resulted in the formation of three large mega-continents, and numerous smaller landmasses and microterranes. The big three were: Laurentia and Baltica located equatorially and massive Gondwana sprawling australly. An elongate assemblage of island-arc, microterranes of Rodinian ancestry became attached to the northern margin of West Gondwana during the Cadomian orogeny. The ribbon of amalgamated terranes is also called a superterrane, with each component named for its ultimate tectonic-destination on the continents of North America and Europe.


    Late Proterozoic Reconstruction of the Southern Hemisphere
    In the latest Proterozoic (550 Ma), Rodinia has fragmented apart forming Laurentia (North America), Baltica (northern Europe) and Gondwana (mostly our South Hemispheric continents) with the opening of the Iapetus Ocean. The peri-Gondwanan terranes of Avalonia, Armorica and others have assembled on the northern Gondwana margin from the craton of Amazonia to West Africa. Many aspects of these paleographic reconstructions are subject to intense debate and ongoing investigation.
    Modified from Cocks and Torvik, 2006.

    Facing the newly opened Iapetus Ocean (more so as Baltica drifts to the north), the “peri-Gondwanan” terranes are categorized as largely Avalonian-type and Cadomian-type, which designates their future accretionary locale after separating, rifting and drifting from Gondwana. One author's interpretation (below) adds the Serindia-type terrane for regions of North China. The Cadomian terranes eventually formed a portion of western Europe's basement carrying its earlier Rodinia rocks in transit. Typical of tectonic processes, plate collisions transport, reimprint and rework their crust.

    Early Ordovician (490 Ma) South Hemispheric Reconstruction of the North Margin of West Gondwana
    This ambitious reconstruction depicts a ribbon-like superterrane, that throughout the Paleozoic beginning in the Devonian, will rift from the northern margin of West Gondwana (at the Amazonia craton of South America and the West Africa craton) and collide with Laurentia and Baltica. Avalonia will depart first closing the Iapetus Ocean and Cadomia second, closing the Rheic Ocean along with the remaining mass of Gondwana. Note that based on paleomagnetic and paleontological data, Armorica (which will form western France) is placed on Gondwana, which appears to remain attached before the Early Devonian. See the paper referenced below for the complete terrane legend in the diagram.
    Modified from Stampfli et al, 2002.

    (2) Avalon-type terranes accrete to Laurentia
    Although this stage is not germane to the formation of the Paris Basin, an explanation would be incomplete without commenting on the destiny of the Avalonia terrane. Throughout Paleozoic time in what's called the "supercontinental cycle," the Gondwana-derived basement blocks sequentially reassembled to form the supercontinent of Pangaea. During the Acadian-Caledonian orogeny (Ordovician to Early Devonian), the Avalonian-type terranes rifted from Gondawana, drifted across the Iapetus Ocean as it closed, and accreted to eastern Laurentia (early or proto-North America). Following the Silurian closure of the Iapetus Ocean, mountains were built from northeastern Laurentia into Scandinavia and parts of north-central Europe. The black outline of the modern continents can be differentiated on the map. At this time, the Cadomia-type terranes remained attached to Gondwana.

    Jumping ahead, when Pangaea later fragmented apart (just as Rodinia previously did), the Avalonia terranes would separate between North America and Europe across the Atlantic Ocean. As a result, we occasionally use the terms of West Avalonia (for the Canadian Maritimes and down the east coast of North America) and East Avalonia (for southern Britain and the Brabant Massif into parts of northern Germany). When new landmasses (and even ocean basins) form and reform, geologists use new names to identify them in time - similar to new countries that are renamed by their new political leaders.

    Latest Ordovician Reconstruction of the Southern Hemisphere
    In the latest Ordovician-Earliest Silurian (440 Ma), Avalonia (both West and East reside at left arrow) has previously rifted from the northern margin of Gondwana, drifted across the closing Iapetus Ocean and is about to collide with Baltica and Laurentia during the Acadian-Caledonide orogeny. The main body of South Polar Gondwana is in the process of traversing a diminishing Rheic Ocean. The Cadomian-type terranes (right arrow) are still docked on the margin of Gondwana.
    Modified from Cocks and Torsvik, 2006.

    (3) Cadomia-type terranes accrete to Laurussia - France's basement!
    By the Permian, the main mass of Gondwana collided with Laurussia (Laurentia + Baltica + Avalonia) in the Ouachita-Alleghenian-Variscan orogeny and assembled the supercontinent of Pangaea. The resulting mountain belt was the largest collisional orogen of the Paleozoic. In Europe, it produced a suture from Germany (Mid-German Crystalline zone) through southern Britain (Lizard ophiolite) through France to southern Iberia (Pulo do Lobo unit). Hence, the Rheic suture separates the Cadomian terranes of western and central Europe from the terranes derived from East Avalonia in Britain.

    The closure of the intervening Rheic Ocean (recall that the Iapetus Ocean closed with the Avalonia collision!) brought the Cadomian-type terranes of Gondwana into contact with Laurussia (red arrow) during the Variscan orogeny (formerly Hercynian). The Variscan and Alleghenian orogenies were contemporaneous and more-or-less physically contiguous. The collision of a Gondwana-derived Europe was forming on Laurussian soil! France was never before so close to French Canada!

    Mississippian Reconstruction of the Southern Hemisphere
    In this Mississippian view (340 Ma), the Cadomian-type terranes (arrow) have rifted from the main body of Gondwana and will collide with Laurussia along with Gondwana (to followmain body of Gondwana and will collide with Laurussia along with Gondwana (to follow) during the Ouachita-Alleghenian-Variscan orogeny. Gondwana's collision formed Pangaea at the expense of the Rheic Ocean. The basement terranes of Europe have now formed - a Gondwana Europe. The only thing left to do is get them across the Atlantic Ocean, which will soon form.
    Modified from Cocks and Torsvik, 2006.


    (4) Variscan orogeny forms a Gondwana Europe within Pangaea
    The Variscan orogeny is building a Gondwana European basement within Pangaea. Its formation left Variscan orogenic remnants and a montage of Cadomian terranes in France and central Europe. As with East Avalonia in southern Britain, Europe's Cadomian basement ended up across the Atlantic when Pangaea fragmented apart.

    Early Permian (280 Ma) Timeslice of Pangaea and Ouachita-Alleghenian-Varsican Orogeny
    Pangaea has fully formed with the collision of Gondwana and Laurentia (actually Laurussia). The Cadomian terranes terranes have accreted in the Variscan orogeny to Laurussia. The Ouachita-Alleghenian-Variscan orogeny is fully underway building the Appalachian Mountain chain in North America. The collision will distribute remnants of the Variscan orogen in France and Europe, and around the Paris Basin, which is about to form in a fore-arc, extensional regime.
    Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

    Thus, the Paris Basin (seen below in Europe) has tectonically-acquired its Cadomian-Variscan crystalline basement. Notice the assembly in Europe of Paleozoic landmasses. Europe's cratonic platform is comprised of a montage of terranes and fault-bounded blocks of continental crust with Avalonian and Cadomian ancestry - a Gondwanan-derived Europe of recycled Precambrian and Cambrian crust. The principal ones that now form Europe are Avalonia, the Rheno-Hercynian Terrane, the Armorican Terrane assemblage, Perunica, Apulia, Adria, the Hellenic terrane and Moesia - all peri-Gondwanan terranes with the exception of Baltica-derived Scandinavia.

    A European Collage of Amalgamated Gondwana-derived, Avalonia and Cadomia-type Terranes
    This map demonstrates the complex accretion history of Europe. For reference, Paris is at the red dot.
    Modified from Ballevre et al, 2008.

    (5) Post-Variscan extension creates epicontinental depocenters
    Following the Permian consolidation of Pangaea, the supercontinent began to fragment apart. The re-activation of pre-exisiting Variscan compressional faults formed new, extensional back-arc rifts in late Permian through Triassic times. In the Triassic, extension led to the opening of oceanic marginal basins. This allowed the development of numerous European sedimentary basins including the Paris Basin in Gondwana Europe. Europe has not yet formed and will not be called as such, geologically, until Pangaea fragments aparts and sends parts of the Avalonia terrane and the entirety of the Cadomia terrane across the Atlantic Ocean.

    Early Jurassic Timeslice (200 Ma)
    The Varsican orogen has left remnants in what will become France and central Europe. Extension within the Variscan's fore-arc regime has already begun to flood with waters from the newly opening North Atlantic Ocean. As the mid-Atlantic Ridge widens and Pangaea continues to fragment apart, Europe and Africa will reside on their own tectonic plates and France will have acquired its Paris Basin.
    Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

    (6) Pangaea rifts apart sending peri-Gondwanan terranes across the Atlantic
    As Pangaea's break up progressed, the Eurasian-North American plates drifted apart sending East Avalonia and the Cadomian terranes across the Atlantic. Beginning in the Permian and while in tectonic-transport, crustal extension continued across Europe with the establishment of a broad, open shelf that occupied much of southern Germany, the North Sea and the Paris Basin. The subsidence of the basins created accommodation space that became the site of sedimentation as the sea level of global high seas repeatedly and episodically fluctuated. Most of the Paris Basin became emergent near the end of Jurassic time, a relict appendage of the large Triassic German basin.

    Late Cretaceous Timeslice (75 Ma)
    The nascent Atlantic Ocean has begun to separate in the north at the Mid-Atlantic Ridge. The tectonic plates of North America and Eurasia are separating. Europe and Africa have formed but are submerged by global high seas. The region of the epicontinental Anglo-Paris Basin is fully submerged,one of many eustatic events that will contirbute to sediment deposition into the many basins of Europe. Notice the various Variscan orogenic remnants distributed about western Europe - France, Spain and Portugal in particular.
    Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

    Today, the Paris Basin is surrounded by outcrops of four Cadomian/Variscan massifs: the Armorican Massif in the west, the Massif Central in the south, the Vosges in the east, and the Ardennes in the northeast. Not only the Seine River network incises the Paris Basin and Cadomian/Variscan basements but those of the Rivers Loire, Meuse and Moselle.

    Paris within the Paris Basin Surrounded by Remnants of the Variscan Orogen
    From CNAM / MNHN: SGF "The Parisian basement: quarries, underground projects and the Grand Paris"
    by J.-P. Gely, 2013

    (7) Global high seas repeatedly flood epicontinental Europe
    The opening of the Atlantic Ocean, beginning in the Cenozoic, had a profound affect on the neighboring North America and Eurasian plates. The main process was a general extensional stretching that produced numerous marginal basins and grabens. Large quantities of clastic materials were deposited in repeated transgression-regressions of the sea within the many depocenters that trended pre-existing structural directions.

    In France within the Paris Basin, during the Late Triassic, siliciclastics were deposited; Jurassic Liassic-time organic-rich black shales, Dogger carbonates and Malm-time clays. The return of the sea in Cretaceous time deposited chalk. Basin sedimentation continued into the Tertiary. With particular interest to this post is the Lutetian age of the Eocene (Tertiaire on the map below and diagram below) with a shallow-water environment conducive to the formation of limestone and evaporite deposits of gypsum.

    Simplified Map of France and the Paris Basin


    (8) Alpine Orogeny shapes and confines the Paris Basin
    The Paris Basin took on its present shape following uplift of the surrounding basement blocks during the Alpine orogeny. The collision occurred between the Africa and Eurasia plates and included the subduction of the intervening Tethyan Ocean. The Alpine orogeny is considered the third major collision to define the geology of Europe in the Late Cretaceous through Recent, along with the previously discussed Caledonian and Variscan orogenies.

    In addition to creating Alpine mountain plate across Europe and into Asia, it regionally caused northwest-southeast compression of the Paris Basin and formed anticlines along genetically-related, basement fault systems. The widespread uplift inverted many basins and served to isolate the Paris Basin. The uplift also profoundly effected the fluvial systems with drainage lines occurring along structural elements. Cretaceous and Tertiary deformation and erosion have exhumed Mesozoic sediments and the underlying basement.  

    The main stages of the tectono-sedimentary evolution of the Paris Basin are summarized below. At least ten major stratigraphic cycles starting with the Mesozoic (Scythian) and five main stages of basin evolution have been identified (Baccaletto) based on subsidence, sedimentary systems, accommodation variations, and paleography, all bounded by unconformities. A close relationship exists between fault geometry and basin evolution, in particular those of Variscan origination and Pangaea rifting-related extension. Following extension, a gradual conversion to an ongoing Late Cretaceous compressional regime ensued. The Lutetian interval (highlighted), that so dominated the deposits discussed in this post, was affected by compression and deformation associated with the Alpine Orogeny.
    Main Stages of the Tectono-Sedimentary Evolution of the Paris Basin
    From Baccaletto, 2010.

    We have one more important gypsum-mining area to discuss located about two miles east of the Montmartre quarries. Like Montmartre, the quarry is inactive and unrecognizable. Inaugurated in 1867 and coinciding with the opening of the World's Fair in Paris, les Parc des Buttes-Chaumont occupies the site between the villages of Belleville and La Villette (right arrow above on the "Ancient Quarries of Paris" map) in the 19th arrondissement.

    Butte is French for “mound,” and Chaumont is a 9th century contraction of “chauve” meaning bald and “mont” meaning mount. The "Bald Mount" acquired its name from its lack of vegetation due to an abundance of clay and gypsum in the soil.

    View of Park of Buttes-Chaumont from the promenade looking north toward the lake and the temple. The residential quarter of La Villette is in the background.

    In spite of its most austere beginnings, today the park is a major local attraction replete with a rocky island topped by a romantic shrine in the middle of a picturesque artificial lake. Evocative of the Alps, it occupies 25 hectares and is the fifth largest park in Paris. Its grounds are overflowing with ornamental trees, waterbirds, and within the lake, an abundance of fish. From a bleak gypsum quarry to an iconic urban park, the history of its metamorphosis is beyond anything imaginable. 

    The Temple of Sibylle in the Park of the Buttes-Chaumont
    A tonemapped, High Dynamic Range Photo 

    The area of the park, being just outside the limits of the toll barrier wall, was mined for gypsum for centuries as was the Butte Montmartre. It was close to the site of the Gibet of Montfaucon, a notorious and malodorous place where 80 condemned men and women could be executed at the gallows simultaneously and their bodies left to dangle on display as a deterrent to crime well after their executions. Later, the desolate quarry became a public waste refuse and sewage dump, and even an abattoir (slaughterhouse) for horses where the remains were left to decompose. The quarry also had an unsavory reputation for harboring thieves and as a shelter for the destitute. It took a tremendous imagination to envision a park on this impoverished site. 

    Photo of the America Quarries by Charles Marville along Rue de Mexico before 1877
     So much gypsum was shipped to Louisiana that the quarry was called the America Quarry. According to urban legend, the quarry provided gypsum to the United States for building the White House, but in fact it was used for domestic construction. When Marville made this photograph, the quarry was still in operation, but it closed by the 1880's. Notice the buildings of La Villette virtually next to the quarry off to the right. Once again, the only people visible are those that are stationary for the long exposure.
    The quarry photographed by Henri le Secq in 1863 showed a desolate, pockmarked lunar-landscape sandwiched between the villages of Belleville and La Villette.

    The site "spread infectious emanations not only to the neighboring areas, but, following the direction of the wind, over the entire city" (Alphand). Amazingly, this most desolate wasteland was transformed into a spectacular garden park as part of the new Paris of the Second Empire.

    Left: Gibet de Montfaucon, 1811.                                    Right: 1811 Rendering horses
    From an article by Francois Choay in the Urban Park magazine, 29, 1975.

    This not so promising site, to say the least, was envisioned by Napoleon III as a romantic garden showcase befitting a capital. Chosen and conceived by his prefect, Baron Haussmann, it was to be the site of a park for the recreation and pleasure of the rapidly growing population of the 19th and 20th arrondissement - the working class of the petit bourgeoisie. Jean-Charles Adolphe Alphand was the chosen landscape engineer to personally execute the remarkable transformation.

    A plan of the Parc des Buttes-Chaumont
    Note the promenades, belvedere, restaurants, artificial lake, central island and its rotunda. A railroad (left) was constructed to bring in soil and supplies. The grotto is at the top center. 

    When Napolean III became emperor in 1852, Paris had only four public parks, all in the center of the city. His vision changed parks such as the Buttes-Chaumont that were not longer the preserve of aristocratic or royal landowners but were open to the public at large. Through their collaboration, what resulted was one of the crowning achievements of the Second Empire as part of the radical renovation that swept through Paris.

    The quarry cliffs likely photographed by Charles Marville around 1865. The key features of the park are beginning to emerge -the gorge-spanning brick bridge and a section of the quarry above what is to be the lake.

    Beginning in 1864, two years were spent in terracing the land. Railroad tracks were laid to bring in 200,000 cubic meters of topsoil. A thousand workers renovated the landscape, digging a lake and contouring the grounds with rambling lawns, gently sloping hillsides, splendid vistas and shaded strolling paths.

    The plan of the park created by Alphand and photographed by Marville. Again, notice the promenades, the carefully landscaped terrain, a restaurant, the supply railroad, the lake, island and temple at the summit.

    Explosives were used to sculpt the gypsum buttes and former quarry into a small mountain 50 meters high on a rocky island surrounded by cliffs. In a corner of the park, a spacious grotto was fashioned with a cathedral-like vault remniscent of the interiors of gypsum quarries seen at Montmartre. Its ceiling was decorated with artifical stalactites. Even a hydraulically-pumped waterfall cascaded into a stepping-stone lined pool that flowed out of the grottoes second opening. And everywhere, mosses and vines hung on its walls.

    Outside view of the grotto from the walking path

    Engineered Nature
    View of the inside of the grotto with its contrived waterfall, reflecting pool and faux stalactites

    The ceiling of the grotto with its faux stalactites and skylight. No bats in this place!

    Even the stone railings that line the paths of the park are faux bois or fake wood intricately stylized with cut branches, bark, leaves and knots, all cast in recently-perfected concrete almost 150 years ago.

    The Roman temple at the top of the promontory was modelled after the Temple of Vesta in Tivoli, Italy

    Two bridges reach the center island - a 63 meter-long, red metal suspension bridge by Gustave Eiffel, the designer of the Eiffel Tower, and a twelve meter-long masonry bridge, known as the "suicide bridge." Unnoticed by most passersby, the alternating layers of gypsum, marl and sandstone are on display on the excavated quarry-flanks of the mountain.  

    It comes as no surprise, certainly amongst geologists who are acutely aware of these things, that geology has a profound affect on the evolution of civilizations, cultures and societies. We have seen on our brief visit to Paris, in a small corner of the Paris Basin, how geography and its mineral deposits of gypsum have shaped the history of politics, philosophy and art within the city and around the world.

    In my next post "Geological Legacies of the Paris Basin - Part II", we will see the affect that deposits of limestone had on the city of Paris. We'll also descend into the dimly-lit catacombs beneath the streets and explore the infamous ossuaries where 6,000,000 exhumed skeletons from the eighteenth century are both interred and on display.

    After returning from Paris, my wife and I drove from Boston to New York City and experienced a most fitting conclusion to our trip abroad. We visited the Metropolitan Museum of Art to see their final exhibition of "Charles Marville: Photographer of Paris." His nineteenth century photographs (425 of them) document the radical transition from the medieval streets of "Old Paris" that led to the broad boulevards and grand public structures of the "New Paris", the one we recognize today. His photos of the gypsum quarries of the Right Bank were incredible. 

    1. European Geography in a Global Context from the Vendian to the End of the Paleozoic by Cocks and Torsvik, 2006.
    2. Growth and Demise of the Jurassic Carbonate Platform in the Intracratonic Basin Paris by Benjamin Brigaud et al, 2013.
    3. Impressionism - 50 Paintings You Should Know by Ines Janet Engelman, 2010.
    4. Le Lutetien: Une Periode Charniere de L'histoire du Bassin Parisien by Par Jean-Pierre Gely, 2009 (on-line on French).
    5. Meso-Cenozoic Geodynnamic Evolution of the Paris Basin: 3D Stratigraphic Constraints by Francois Guillocheau et al, 2000.
    6. Middle Lutetian Climate in the Paris Basin: Implications for a Marine Hotspot of Paleodiversity by D. Huyghe et al, 2012 (on-line). 
    7. Neoproterozoic-Early Cambrian Evolution of Peri-Gondwanan Terranes: Implications for Laurentia-Gondwana Connections by Murphy et al, 2003.
    8. Overview of the Subsurface Structural Pattern of the Paris Basin by Baccaletto et al, 2010.
    9. Paleography of Europe, DVD Collection, Ron Blakey, Colorado Plateau Geosystems, Arizona, USA.
    10. Paleozoic Evolution of the Pre-Variscan Terranes: From Gondwana to the Variscan Collision by Stampfli et al, 2002.
    11. Paleozoic History of the Armorican Massif by Michel Ballevre et al, 2008.
    12. Paris Basin (Chapter 32) by Alain Perrodon and Julien Zabek, undated.
    13. Paris Reborn - Napoleon III, Baron Haussmann and the Quest to Build a Modern City, by Stephane Kirkland, 2013.
    14. The Formation of Pangaea by G.M. Stampfli et al, 2013.
    15. The Rheic Ocean: Origin, Evolution, and Significance by R. Damian Nance, 2008 (on-line).
    16. Urban Design and Civic Spaces: Nature at the Parc des Buttes-Chaumont in Paris by Ulf Strohmayer, 2006 (on-line).
    17. Vincent van Gogh - Moulin de la Galette by Simon C. Dickinson, 1023 (on-line).

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    "...Paris has another Paris under herself…which has its streets, its intersections,
    its squares, its dead ends, its arteries, and its circulation”
    Les Miserables, Victor Hugo, 1862


    For a discussion of the tectonic evolution of the Paris Basin, its Lutetian stratigraphy and the gypsum deposits of the Right Bank, please visit my previous post entitled "Geological Legacies of the Paris Basin: Part I - Plaster of Paris, the Windmills of Montmartre, the Park of Buttes-Chaumont and a New Artistic Creativity"here.

    Stroll the narrow cobbled streets and broad boulevards on the Left Bank of the old French capital. Enjoy Paris’s beautiful storefronts, its exquisite monuments, museums, parks and stunning architecture. Languish in a sidewalk café or dine in a fashionably chic bistro. For the casual observer, it’s impossible to imagine what lies underfoot – 20 to 25 meters below street level.

    Paris is a city of layers – both above ground and below. Its underground has many new additions, while others are vestiges of the past, often lost and forgotten. Some are accessible to the public, and others have been sealed for an eternity.

    There are Roman Empire foundations and more recent wartime shelters, medieval basements and mysterious church crypts, musty wine cellars and shadowy mushroom farms, subterranean shopping malls and modern multi-level car parks. Factor in 1,305 miles of storm drains and sewers, 133 miles of Métro and RER railway tunnels, and countless miles of utility lines and pipes for water, gas, electricity and telephone. Standing on the streets of Paris, you'd never suspect what exists below you unless you looked at a map of the underground that mirrors the landscape above.

    Modified from the Atlas du Paris Souterrain– a highly-recommended source of information!

    Yet, there exists an even deeper layer! On the Right Bank, the buttes of Montmartre and Belleville are riddled with gypsum quarries. On the Left, Paris is honeycombed with a labyrinth of over 200 miles of cavernous limestone quarries replete with a macabre section known as the Catacombs – after the ones in Rome.  

    The Catacombs is a dimly lit, musty maze of galleries and corridors lined with the bones of 6,000,000 (seven by some counts) disinterred Parisians. In one section, a water-filled well contains the stratigraphic contact of the Lutetian age 45 million years ago. How did these two “cities” evolve? How do they co-exist? A luminous City of Light above another of shadows and darkness.

    The city of Paris occupies a tiny portion of the extensive Paris Basin – a 140,000 square kilometer shallow epicontinental trough of flat valleys and low plateaus in the north of France. On a larger scale, the depocenter of the Anglo-Paris Basin that spans the English Channel into Great Britain resides on the continental shelf of the Eurasian plate. Its foundation is a Late Proterozoic Cadomian-late Paleozoic Variscan crystalline basement. Please visit my post Part I for the Paris Basin’s juicy tectonic details here.

    Paris (red dot) within the extensive Anglo-Paris Basin on a
    Jurassic through Neogene Surficial Geology Map
    During the late Paleozoic, the basin began to form subsequent to extensive orogenic collisions that formed Pangaea in the western hemisphere. By the end of the Mesozoic, the basin (along with the assemblage of France, Belgium, Great Britain, Scandinavia and Western Europe) was tectonically transported to the eastern hemisphere on the Eurasian plate when Pangaea fragmented apart and the Atlantic Ocean opened its waters.

    The basin’s strata were deposited in a multitude of Tertiary age transgressions and regressions of tropical seas that flooded the epicontinent of Western Europe. Formed in a mixed environment of marine, coastal, lagoonal and freshwater conditions, deposition was followed by compaction, cementation and eventual lithification.

    Modified from Ron Blakey and Colorado Plateau Geosystems, Inc.

    The sedimentary rocks that formed - during the Eocene epoch in particular - built the city of Paris: Bartonian age gypsums (gypse) for plaster of Paris on the Right Bank (north side of the river Seine) and Lutetian age limestones (calcaire grossier), chalks (craie) for lime-based cements and paints, clays (argile) for tiles and bricks, and sand (sable) for masonry on the Left Bank (south of the river). The deposits on each side of the river Seine are between two low plateaus, Montmartre and Montparnasse. Both banks were exploited from under the city, as Paris grew and expanded on the surface.

    Fortuitously for Paris’s architectural future, the axis of the Tertiary age anticline of Meudon (red dotted line below) passes south of the city. The flexure allowed for the excavation of Paris’s geological bounty of gypsum from the Right Bank and deeper, coarse limestone from the Left.

    Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013

    The geologic transect (black line above) extends across the basin from north to south and is represented cross-sectionally below. Note the availability of Lutetian limestone (calcaire grossier) south of the Seine on the Left Bank and gypsum (gypse) north of the Seine on the Right Bank in Montmartre. The vertical scale across the basin is greatly exaggerated making Montmartre appear like the Matterhorn.

    Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013

    Thus, gypsum has been extracted in the hills of Paris on the Right Bank from Menilmontant, Montmartre and Buttes-Chaumont areas of the 18th, 19th and 20th arrondisements, respectively. Limestone was mined under the small Parisian hills of Montparnasse, Montsouris, Montrouge, the Butte aux Cailles and the Colline de Chaillot, largely on the Left Bank.

    Topographical Considerations of Paris
    Modified from

    The areas of Right Bank gypsum (green clusters) and largely Left Bank limestone (red) exploitation can be seen highlighted on this old Paris map of 1908. The direction of flow of the River Seine is shown in black arrows.

    By 53-52 BC, the Romans had conquered Gaul (roughly France and Belgium) and the Celtic Iron Age tribes living in the region. Within the Paris Basin, that included the Parisii, living on the banks of the river Seine. The Romans called their settlement on the hills south of the river Lutetia Parisiorum or Lutece in French. The name was derived from a Parisii word meaning marsh or swamp. In turn, geologists borrowed the name for the Lutetian age - a division of the Eocene epoch of the Cenozoic Era- the time in which the limestone called “Paris Stone” formed – 47.8 to 41.3 million years ago.
    The decision to settle above the banks of the Seine was governed by its ideal location for trade, defense and availability of raw materials especially water and the limestone for Roman buildings, military fortifications and roads. The Roman and Medieval era that followed produced lasting design elements for the development of the city from the Renaissance through the 21st century.
    Please note the Roman open quarries (right) in the vicinity of the River Bievre near its confluence with the Seine (lower right), and the Arenes de Lutece amphitheater. As a modern reference, the island in the middle of the Seine in the upper right corner is Île de la Cité that houses the Cathedral of Notre Dame.
    The Romans in the 1st century and the early Parisians through the end of the 12th century acquired coarse limestone for structures in the most instinctive of ways – from above ground where it was most convenient. It was removed from open quarries (carrières à ciel ouvert) where it had been exposed by erosion such as the region of the Seine’s ancestral tributary, the Bievre (see above). The technique was primitive, but the rock was readily available and had existing natural fractures that facilitated its extraction.
    One such quarry, virtually unrecognizable today, lies within the heart of Paris beneath the Arena of Lutece, a partially restored Roman amphitheater. Once considerably larger, the majority of the arena’s limestone has been repurposed into structures subsequently built throughout the millennium.

    By the end of the 12th century, medieval Paris had become a medium-size, walled city with a population of 25,000 surrounded by countryside of farms and vineyards. The extraction of surface limestone was gradually replaced by underground workings to satisfy the sharply increased needs for building construction such as Notre-Dame Cathedral, the Louvre Palace and the ramparts of the city.

    Mining below the surface also minimized the excavation of overburden, allowed deeper fine-grained deposits to be reached and conserved topsoil for farming immediately around the growing city. The first underground excavations were essentially extensions of the open quarries by digging horizontally into a hillside exposure (left diagram).
    Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013
    The first mining method employed the “room and pillar” technique, called piliers tournes. After a horizontal tunnel was excavated, perpendicular and then parallel tunnels were added (right diagram). The result was a maze of interconnecting passageways with the weight of the ceiling supported by a grid of massive columns of untouched, solid limestone. It helped to prevent collapse of the undermined roof, but a significant portion of usable excavated material was lost.
    In the 15th century, vertical wells were sunk and then tunnels were dug horizontally from there. In order to raise limestone blocks to the surface, wheeled wooden winches reminiscent of “squirrel” wheels were driven by workers climbing rungs, oxen or horses to raise blocks of limestone vertically. The system could haul up large slabs that weighed as far as 30 meters down. 
    Modified from M. Vire of MNHM and Jean-Pierre Gely, 2013
    These mining techniques were also used on gypsum deposits for plaster of Paris in Montmartre and the Belleville hills on Paris’s Right Bank. Although artificially engineered, the grotto at the Park of the Buttes-Chaumont is reminiscent of the cathedral-like excavation structures that undermine the region. Please visit my previous post regarding gypsum excavation on the Right Bank here.
    In the 16th century, the mining method of hagues et bourrages was employed that was economically productive and structurally sound. Instead of tunneling horizontally into the exploited table of limestone, miners would extract stone progressively outward from a central point. When the ceiling became sufficiently unsupported, a line of stacked piliers a bras was erected from the floor to the ceiling. When extraction continued outward, a second line of stone columns was added, which were then transformed into walls or hagues as the space in between was backfilled with waste rubble or bourrage.

    For a fantastic and imaginative 3-D tour of the evolution of Paris beginning with the early Celtic settlement, check out the video here.  A fine appreciation will be gained for the volume of limestone that was extracted beneath the Left Bank during the building of the city.
    The first underground limestone quarries were located in Paris's suburbs (faubourgs) on the Left Bank. As the city continued to grow, new underground quarries with interconnecting galleries were developed on the city’s expanding periphery. Old abandoned quarries fell into oblivion and were gradually built over.
    Although the undermined state of the Left Bank was known to city architects in the early 17th century, Parisian’s became painfully aware of their precarious existence over the subterranean voids when they began to cave in. At first many thought it to be the work of the devil. Called subsidence sinkholes (fontis in French), the cave-ins varied in size with some affecting houses and others affecting entire streets.
    Formation and Evolution of Subsidence
    A fontis is a cavity that develops when the roof of a subterranean gallery caves in.

    A cloche is the rounded top of the rubble pile.
    Modified from Daniel Munier and from M. Vire
    The arched void forms that migrates upward as the ceiling rocks gradually tumble in. When the sinkhole finally breaks through the surface, the rounded top of the rubble pile or cloche can be viewed within the sinkhole from above - giving the cavity that has formed a bell shape. These sinkholes should not be confused with those that occur in a karstic landscape, which develops under a cover of soluble rocks - also limestone - via acidic water that has acquired atmospheric carbon dioxide.   
    When the largest collapse occurred in 1774, a wave of panic spread through Paris. A giant sinkhole catastrophically swallowed a busy Parisian neighborhood including roads, buildings, houses, horses, carriages, oxcarts and throngs of people along Rue d’Enfer (now called Boulevard Saint Michel near Avenue Denfert-Rochereau). Appropriately, enfer is the French word for “hell,” and the gaping hole in the earth became known as the “mouth of hell.” The quarries that built the city of Paris were literally threatening to destroy it - neighborhood by neighborhood.

    How ironic! The limestone that went into the construction of Notre-Dame, the Palais-Royal and the mansions of the Marais on the surface of Paris actually had come from the quarries beneath Rue d’Enfer – now taking revenge upon the city.
    “Paris (had) begun to devour its own foundations – sand for glass and smelting,
    gypsum for plaster, limestone for walls, green clay for bricks and tiles.”
    From Graham Robb’s “Parisians: An Adventure History of Paris”

    In response to the fear of collapse, King Louis XVI designated a commission to investigate the state of the Parisian underground on April 4, 1777. It was called the Inspection Unit for Quarries Below Paris and Surrounding Plains. The head of the newly minted office - appointed by the King by chance of fate only a few hours before the collapse - was an architect named Charles-Axel Guillaumot, who held the position of General Inspectorate of the Quarries (IGC) until his death in 1807 - in French, Inspection Générale des Carrières.
    “Guillaumot inspected the "gaping wound as an explorer
    could contemplate the shores of a new continent.”
    Author Graham Robb

    This “Savior of Paris" that the city owes so much set about to inspect and map the fragile voids under the entire city, many of which were illegal and uncharted but most abandoned and forgotten. His goal was to excavate them where needed and reinforce (consolidate) them from future collapse. Virtually every chamber was mapped and assigned a name that corresponded to the street above. The inspected walls still bear his chiseled signature, a "G" and date.


    Following in the tradition of Guillaumot, engineers from the Inspection des Carrieres generally signed and dated their consolidation projects by carving their initials, order number and the years the work was carried out into the walls. Fleur-de-lis, the royal symbol of the French Empire, were obliterated from most of the signatures during the French Revolution.
    In order to safeguard public roads and of course the King’s properties, Guillaumot erected pillars from the quarry floors to their ceilings, “retrospectively-created foundations for the edifices built on the surface” (Gilles Thomas). The result was that every undercut surface street was doubled by a gallery that followed the same layout. In a sense, Paris became a mirrored city with one above ground and the other below. This allowed the evolution of subsidence voids to be monitored and shored up as needed. The same can be said of the modern city of Paris with its underground double. Here's an example from the 13th arrondissemont.
    In Guillaumot’s own words:
    “To monitor the preservation of these constructions at all times,
    It was necessary to render them accessible; to this effect,
    a gallery wide enough to allow passage of construction materials was left under
    and within the public way; at the gallery’s farthest point, another wall was built.
    Perpendicular galleries were dug here and there to enable communication between
    both sides of the public way and to allow movement from one gallery to the next.”
    (Memoirs on the Work Ordered in Quarries in Paris and Adjacent Plains, 1804)
    Another peril was threatening the city – an insidious one that had become equally intolerable and every bit as dangerous. Paris’s cemeteries had become horrifically overcrowded. The earliest burial grounds were on the southern out-skirts of the Roman-era city on the Left Bank - outside the city! By the 4th century, burials had moved to the Right Bank on filled-in marshland - within the city. In particular was the property of the Saints Innocents church in 1130 - named after the biblical narrative of the "Massacre of the Innocents" by Herod the Great, the Roman-appointed King of the Jews.
    No larger than a city block and literally within a few blocks of Notre-Dame in the midst of Paris’s densely inhabited area in the current district of Les Halles, problems began to pile up, literally. The foundation of Paris’s first Christian churches were somewhat removed from the center of population and many became crypts for those seeking a final resting place closer to god, a service only available to the wealthy. Common folk were buried outdoors on consecrated clergy property, close to their creator in the "fresh" air. One would think! 
    Map of Paris in 1550
    The Cemetery of Saint-Innocents is circled for reference. Click for a larger view.
    Modified from in the Public Domain 
    Saint-Innocents had become Paris’s principal cemetery, although there were countless burial grounds in the city. Saint-Innocents was adjacent to the city’s  principal marketplace Les Halles, where fresh farm products were sold daily. Burying the dead in town was a radical departure from the norm, contrary to logic, sound urban planning and public health.
    The red ellipse encompasses the Cemetery of Saint-Innocents that included the central burying ground, the church and the surrounded charnel house. Notice the proximity of Saint-Innocents to the central market Les Halles - now known as Forum des Halles. This ambitious, aerial urban map of 1739 before the city’s redesign by Baron Georges Eugene Haussmann is but a small section of Paris with accurate detail of every building drawn down to the windows. You can visit the entire city map here.

    Turgot-Berez Map Plan of Paris in 1739
    Modified from

    By the end of the 19th century, the burial ground in Saints-Innocents has become a two and one half meter-high mound filled with over ten centuries of dead bodies largely from Paris’s 22 parishes – perhaps two million. The corpses had accumulated from natural causes, disease (particularly cholera and plague), famine, wars, and the collected remains from hospitals such as the Hôtel-Dieu and the morgue. Other Parisian parishes had their own burial grounds, but the conditions in Saints-Innocents were by far the worst.

    In an attempt to relieve the overcrowding, Saints-Innocents was enlarged and surrounded by a high wall. What had begun as a cemetery of individual sepulchers - burial chambers such as crypts and tombs - had become a site for mass graves with large numbers of bodies buried in a single pit. When a mass grave was filled, a new one was initiated. And so on.

    To make room for more burials in the 14th and 15th centuries, charniers or charnel houses (from a Latin derivative relating to flesh) were constructed around the burying ground to act as a repository for the overflow of corpses from the burying ground.


    The long dead were exhumed and their bones were tightly packed into the walls and roofs of the charnier galleries. Bones were stacked in an almost artfully decorative pattern, while outside, rotting corpses on the grounds poisoned the air with a nauseating stench. Those living in proximity to the cemetery and certainly those downwind were the first to suffer. Broth and milk were said to sour within hours. The tapestries of merchants in nearby Les Halles discolored quickly. Wine turned to vinegar and resting one’s hand on damp, moldy walls was a risky endeavor. In nearby churches, the generous use of incense was insufficient to mask the foul stink. The French writer Louis-Sébastien Mercier (1740-1814) wrote:
    “The stench of cadavers could be smelt in almost all churches;
    …the reek of putrefaction continued to poison the faithful.
    Rats live among the human bones, disturbing and lifting them,
    seeming to animate the dead as they indicate to the present generation
    they among which they will soon stand...
    They (the bones) will soon all turn to chalky earth.”

    A close up of the charnel house shows the skulls stacked in the upper tiers, while rotting corpses literally littered the burying grounds. Now lost but recorded in manuscripts, a mural of Danse Macabre or the Dance of Death was painted on the south wall within an alcove of the charnel house. Represented in many languages and countries, the theme dates from 1424-24. No matter one’s station in life, the universality of death depicted in the “dance” is an artistic genre of late-medieval allegory. It was meant to remind people of life’s fragility and the vainness of the glories of their earthly lives. One might think that a view of the burial grounds was likely all that was needed!

    Further insight into the unhealthy conditions at Saint-Innocents can be gleaned from Mercier’s description of the insalubrious state of affairs at the hospital Hôtel-Dieu on nearby Île de la Cité:
    “Hôtel-Dieu has all it takes to be pestilential (contagious), because of its damp and unventilated atmosphere; wounds turn gangrenous more easily, and both scurvy and scabies wreak havoc when patients sojourn there. What in theory are the most innocuous diseases rapidly acquire serious complications by way of the contaminated air;
    for that precise reason, simple head and leg wounds become lethal in that hospital.
    Nothing proves my point so well as the tally of patients who perish miserably each year
    in the Paris Hôtel-Dieu…a fifth of the patients succumb; a frightful tally
    treated only with the greatest indifference.”
    Nothing was done to remedy the intolerable situation until King Louis XV initiated an investigation in 1763. His successor, King Louis XVI, in his first year on the throne in 1775, issued an edict to move the deceased out of the city. The church resisted the notion, which profited from burial fees. Business was good! To reduce the number of burials, the price was increased, something only the wealthy could afford.
    In 1780, a mass grave containing over 2,000 partially-decomposed bodies collapsed under the sheer weight spilling into an adjacent basement on Rue de la Lingerie. The event further heightened concerns for public health and hastened the decision to eliminate Saint-Innocents once and for all.  That same year the edict was issued that forbade burying corpses at Saint-Innocents and all other cemeteries within the city limits of Paris.
    At a time when Saints-Innocents housed over two million corpses, one major problem had been solved, but a greater one was created. What to do with the overflowing contents of Saint-Innocents?
    Mine consolidations were still under way and included the addition of a network of interconnecting subterranean passageways for access. With the cemeteries closed, Police Prefect Lieutenant-General Alexandre Lenoir supported an idea of moving the dead to the newly renovated corridors to be used as an underground sepulcher. The idea became law in 1785. Saints-Innocents was to be evacuated and converted into the public square that has remained to this day, Place Joachim-du-Bellay – more on that story later in this post.
    The location for the collective burial ground was a spot designated in popular culture as the Tombe-Issoire within the limestone quarries of the Montrouge Plain outside Paris - more precisely, the suburb of Petit-Montrouge. The region is on the hillsides on the left bank of the Bièvre River mentioned earlier and riddled with limestone quarries at depth. At the time, the commune was outside the city walls of the Wall of the Farmers-General, used primarily for tax collection rather than defensive purposes. It was variously known for its monasteries, religious orders, royal hunting grounds, windmills and, of course, its quarries. Today, there are no famous monuments in the suburb of Montrouge. The major tourist attraction is beneath the quarter! 
    The location of the Plains of Montrouge outside the walls of the city of Paris
    On April 7, 1786, the grounds of the former quarries of the Tombe-Issoire under the Plain of Montrouge (the burial site of a legendary giant named Issoire slain by William the monk) were sanctified in the presence of the church abbots, the architects of the project and Charles-Axel Guillaumot. On November 16th, Monseigneur Leclerc de Juigne and Archbishop of Paris ordered: 
    “the removal of the Saints-Innocents Cemetery, its demolition and its evacuation,
    entailing the turning of the soil to a depth of five feet and the sieving of earth,
    with any remaining corpses or bones to be transported and buried
    in the new underground cemetery of the Montrouge Plain.”
    Cited in Les Catacombes, etude historique, 1861
    The Tomb was called the Catacombs of Paris, in French, Les Catacombes de Paris, after the Roman Catacombs. Although Paris’s early limestone quarries date back to the Roman period, the Catacombs do not. And, unlike the Roman Catacombs, they were never excavated for the purposes of burial, only repurposed for burial after the space had been established. The official name for the catacombs is L’Ossuaire Municipal or The Municipal Ossuary.  
    The first transfers of bones from Saints-Innocents to the Catacombs lasted 15 months and continued with the populations of Saint-Étienne-des-Grès, Saint-Eustache, Saint-Landry, Sainte-Croix-de-la-Bretonneries, Saint-Julien-des-Ménétriers and so forth. Continuing to 1814, every cemetery, church ground, crypt and tomb of Paris was nocturnally emptied of its human remains. In total, over six million Parisians were withdrawn and transported to their new “haven of peace” beneath the Plains of Montrouge. The exact number is impossible to determine. The estimate is based on the number of burials up to the year 1860 when the contents of the last graves were transferred to the ossuary. 
    The enormous transportation of bones was scrupulously ritualized and conducted at nightfall. Torchbearers followed by priests wearing surplices and stoles accompanied funerary carts draped in black sheets while chanting the Mass of the Dead. The poet Gabriel Marie Jean Baptiste Legouvé (1804) described the procession as a “shapeless debris-monument to the departed.”

    The Catacombs of Paris lie some 20 meters beneath the south Paris suburb of Montrouge. The town bears little resemblance to the former bucolic royal hunting ground on the Plain of Montrouge. In fact, one must look hard to identify buildings of “old” pre-Haussmann Paris, but they’re there. In fact, you arrive beneath one if you take the Paris Métro at Denfert-Rochereau station, and you must enter one in order to descend into the Catacombs!
    A good landmark on the street is the bronze statue called the Lion of Belfort within the square, now auto-roundabout. Theatergoers may recognize it as the backdrop at the beginning of the third act of La Bohème by Puccini. General Pierre Philippe Denfert-Rochereau (nicknamed the Lion) achieved fame by courageously fighting against the invading Prussians in 1870 at the city of Belfort in northeast France. Anxious to put a positive spin on his defeat and looking for heroes of the conflict to glorify, French authorities erected the majestic statue in the center of Place Denfert-Rochereau. By the way, the statue was created by Auguste Bartholdi, the father of the Statue of Liberty. 

    Place Denfert-Rochereau was previously known as Place d’Enfer or the “Place of Hell”, the street of the infamous collapse of 1774. Rue Denfert-Rochereau was formerly called Rue d'Enfer or the “Street of Hell.” “Denfert” and “d’Enfer” are pronounced exactly the same, a coincidence too perfect for the Paris city hall to ignore when they changed the name - an apparent municipal pun. Interesting sense of humor those French.
    Here the square and the lion on a 1932 map of Paris. Notice the green space immediately to the west of the Place Denfert-Rochereau. It's the Montparnasse Cemetery. After all cemeteries had been banned in Paris for health concerns, several new cemeteries outside th