(This article is part of a new series titled “My Life with Stone”)

On Earth Day last year, I was thinking about the health of our planet, but also about its age and the changes it has been through. I also thought, as I sometimes do on Earth Day, of the scientists who have been documenting the evolving nature of our airy, watery, rocky world that has the moving parts of a fired-up dynamo below its crust. I checked my notes from last year, an Earth Day when we were fresh into the pandemic and the practice of staying home. Last year I ventured out anyway for a necessary meeting, and along the way, I enjoyed the free flow of thought that may visit when you’re alone in the car.

Stromatolites at Lester Park, Greenfield, NY

For me, Earth Day 2020 opened sunny with Mr. and Mrs. Cardinal in my birdfeeder. Below them, a thin snow frosted the new April-green grass. Coffee-cup in one hand, the other on the wheel, I saw the snow cover disappear as I left its realm, driving down the slopes of the escarpment I live on. The snow cover was gone well before I met my colleague in Ballston Spa in the valley of Kaydeross Creek. But the snow being an elevational event, and the day remaining cool, the April dusting was still on the ground later when I ascended the back roads through Milton and Greenfield to the office where I had been working regularly lately. My home office. The trip had taken me over craggy slopes and ridges formed of Cambrian-age rock. The Cambrian period began a little more than half a billion years ago, a time when there was an “explosion” in the diversity of life on earth. Nearly all animal phyla in today’s world (plus some others that died off along the way) had their origins in this prime evolutionary event. Along the way, a closed-road detour took me past Lester Park, a New York State Museum property where you can pull over, and on the surface of the exposed bedrock, you can see the fossils of Cambrian stromatolites, rock structures originally composed of algae strands and trapped sediment that existed in an ancient sea 490 million years ago.

Schoharie floodplain from the eastern escarpment looking toward the west valley wall

As I drove, my mind’s morning reverie took me back to the Village of Schoharie, to the highest terrace of Schoharie Creek nestled against the bedrock slopes of the eastern valley wall. I stood here a few years ago with my archaeological survey crew and our consulting geologist while a backhoe dug deeper and deeper into what is essentially an ancient floodplain left perched when the creek eventually cut down and away. The Schoharie abandoned this terrace long ago as it migrated across the valley toward its other wall, another immense formation of bedrock that had been an ocean floor before it was elevated by the immense world-building forces that move through our old Planet Earth. Such forces have quite an effect over time, although minute-to-minute, day-by-day, in our usual experience we think of the earth’s lands and waters as more or less stable. The rising and falling tide is a big deal from this perspective. But 100% of this perception is, as Yogi Berra might have said, at least 50% mental. It’s a default setting in our assumptions. Sometimes, shaken by earthquakes, blasted by hurricanes, or confronted by chunks of North America’s eastern side collapsed by the surging Atlantic, we get more than a little impressed with the earth’s dynamics.

Trowling and inspecting a Schoharie trench wall

Creeks that migrate directionally for millennia deposit less and less sediment over time in the direction of their old terraces. Meanwhile, they cut new channels and build fresh terraces at a series of dropping elevations, the lowest and youngest always next to the creek. We were working on the first terrace to be abandoned by the Schoharie, and a deep sequence of sediments had built up there. Large loads of silt and sand were deposited at first, but deposition thinned and slowed down considerably 2000-3000 years ago (based upon the age of Native American artifacts found in the upper soil levels, compared to the age of radiocarbon-dated charcoal from deep in the terrace). Only the top couple of feet of silt were deposited since the rate of deposition had slowed so substantially. This depositional situation reflects the present-day distance to the creek on the other side of the valley, where it remains except when it comes roaring back, like it did when Hurricane Irene’s flood covered our Schoharie site in 2011. When we were there a couple of years later there was still flood debris such as pieces of lumber stuck in honeysuckle branches five feet off the ground.

At a depth of 10 to 11 feet below the ground surface, the backhoe encountered a mass of charcoal and spread it on the excavated soil laid out next to the test pit. It was rather a small mass as far as burned chunks of trees go, but it was significant to us. There were no associated Indian artifacts from that depth. The consulting geologist felt that the charcoal had been washed downstream and deposited by a massive flood of the Schoharie (At the expense of being repetitive, the Schoharie’s floods are well known for their floodplain-gouging, alluvium-dumping, bridge-bashing severity). When we learned the age of the charcoal from radiocarbon assay it was 8110+/-40 radiocarbon years before present (BP). But the age is actually older than it sounds. Radiocarbon dates get calibrated because they diverge from calendar dates. The old ones are rarely as close to calendar dates as we might imagine. The calibrated date is 7103 BC (9053 BP), some 900 years older than the radiocarbon age. This date is an average (median) of the probabilities affecting the age determination of this radiocarbon sample. But I simply like to call it 7103 BC.

7103 BC! Wow, that’s old! Especially in terms of the human history of eastern New York State, where early evidence of occupation is still scarce, and data on its environmental context are always welcome. A couple of years earlier, we had found a hearth about that old constructed by early Indigenous people in the present-day Town of Wilton, Saratoga County. The firewood burned there was pine, a fact that adds just another little bit of environmental information to the human history of this period. Pollen data from across the northeast indicates that one kind of forest followed another. Extensive pine forests were pretty early, and pine was the wood burned in the Wilton hearth. The radiocarbon date is calibrated to 7802 BC (8760 +/- 40 BP). The general assumption I have heard paleoethnobotanists make is that people used the most available wood for their fires rather than necessarily the best wood. Otherwise, these early Wilton residents could have searched for birch, a hardwood relatively common then, and found it (presumably) farther away.

But I digress. 7103 BC and 7802 BC are old but not that old. Not really, although they are respectably old on an archaeologist’s time scale. The aforementioned Lester Park, near Saratoga Springs, is 490 million years old. Also, you don’t have to go far from Saratoga or Schoharie to see other, especially dramatic effects of the restless earth as they played out in eastern New York over hundreds of millions of years. From Schoharie, you can drive south on Route 30 to Middleburgh, where you intercept Route 145. When you head into the hills on Route 145 you follow the course of the Little Schoharie Creek to its source in a strikingly beautiful body of water and wetland referred to as Vlae Pond. Here, high in the hardscrabble hills, you cross the drainage divide. Remarkably, Vlae Pond also gives rise to Catskill Creek, which flows in the opposite direction of the Little Schoharie. Catskill Creek descends southeasterly through a widening valley and eventually finds sea-level at the Hudson River estuary. Along the way, it cuts through the rugged landscape of the Hudson Valley Fold-Thrust Belt. In the road cuts of Route 23 in the Fold-Thrust Belt you can see the rock strata uplifted and folded tight like a closed accordion bellows, silently testifying that we live in a dynamic world where, with enough time, ocean floors can turn into mountains, ridges, and valleys. If not for dynamite-blasted passages deep through the rock, this would be a very hilly ride indeed.

The Hudson Valley Fold-Thrust Belt (FTB) is a narrow area of folds and thrust faults created as a result of plate tectonics. Sometimes thrust sections and folding leave the strata out of order. Displayed horizontally across the landscape, the stratigraphic order of the FTB is a distortion of the vertical layer-cake stratigraphy laid down as sediments in Devonian-age seas 380 million years ago (give or take 20 million years). The FTB’s rocks were formed following the westward erosion of earlier rocks when mountains that had risen up east of the present-day Hudson River slowly washed into marine environments. Washed away grain by grain, as the geologists Chet and Maureen Raymo have taken care to note. The sediments were compressed, hardened, and eventually distorted deep in the earth. The metaphor of Deep Time in earth’s history, brought to public awareness by John McPhee in Basin and Range, applies here. The sense of the enormity of time is brought to human consciousness aptly by great depth, as in strata buried far down long ago while seas received eroded mountains in tiny particles.

Folded stratigraphy in an FTB ridge, Route 23 road cut, Catskill, NY. The once horizontal layers are now folded to vertical.

Eventually, the layers piled deep were compressed by weight into rock. Later, they were lifted up from pressure exerted by colliding continental plates (possibly the collision of Africa and a large mass that included North America). Deeply buried strata came to the surface again. Lifting, folding forces tilted the rock layers and pushed them and structured them as parallel ridges, where exposures of older rocks and younger rocks are arrayed horizontally across the landscape in patterns comprehensible but strikingly divergent from the buried layer cake one imagines in order to keep their ages straight. This happened because our old world’s history is, as Stephen Jay Gould eloquently noted, a record of “ceaseless motion”. Ceaselessly moving, Africa’s and North America’s parents crashed into each other. Eventually, the spreading floor of the most recent ocean, the Atlantic, separated the land areas of these continents so far apart that both cleverness and a great diversity of data were required to discover this piece of earth history. No one has ever seen any of this happen directly because the human lifespan is considerably less than 100 million years. But ceaseless motion doesn’t cease. In contemplation of Earth Day, we can assume without risk that the rain will fall, erosion will carry away mountain ranges in tiny pieces, sedimentary rock will form below the ocean, sea floors will spread, continental plates will move, turn, push, and new mountains will rise up to accommodate all of this.

A band of dark grey chert in Kalkberg limestone, Catskill NY

These processes ended up having great import much later for the ancient human history of the Hudson Valley. Broadly across the valley, various uplifted, folded, or tilted ridges have exposed bands of chert. Once people entered the area, some 13,000 years ago, they were attracted to sources of chert, which provided the raw material of sophisticated and complex stone tool technologies. On the western edge of the Hudson Valley, chert sources occur in the Devonian age Kalkberg and Onondaga limestones that outcrop in the FTB ridges and valleys. Chert in these limestones is accessible for human use because of what happened in the FTB’s Deep Time geological history. East of the FTB, ridges related to older geological events, such as the famous Flint Mine Hill and the Paleoindian-age West Athens Hill contain Normanskill (Mount Merino) chert formed in Ordovician shale. People used the cherts closest to them, but they also moved chert around in their travels. Sometimes they carried it (or exported it) well outside of the Hudson Valley.

The many bedrock chert sources in this area created a phenomenal toolstone abundance for ancient Native Americans. But in a remarkable coincidence, quite random with respect to the Devonian (380 million-year-old) deposition and the subsequent folding processes of the FTB, earth’s history piled abundance upon abundance in this area. Much closer to today in geological terms, that is, within the last 20,000 years, glaciers that had picked up rocks and soil as they flowed south began to melt, dropping till (a mix of silt, clay, gravel, and rocks) onto the landscape. “Trillions of tons” of till in McPhee’s words. As they did so glaciers left a legacy of “glacial erratics”, large chunks of rock boosted from the north by the advancing ice. In the FTB, glacial erratics often plopped down along the ridges and valley slopes where chert already was exposed by the fold-thrust dynamics. In one exciting archaeological study area where I have been working, glacial erratics added Onondaga chert to the landscape that already had exposures of Kalkberg chert in the folded bedrock.

A chert nodule in a glacial erratic, Catskill NY

I have visited this Catskill Exit 21 development project study area for archaeological surveys several times since 2015. In the fall of 2019, once again in the field with an archaeological crew, I began to consider how our excavation was uncovering evidence of the latest epoch of earth’s history, the Anthropocene. Elizabeth Kolbert discussed what the Anthropocene might be in her book The Sixth Extinction. The emerging consensus at the time of her writing was that the Anthropocene is the epoch defined by a distinct, human-created stratigraphic signature, just as distinctive fossils in Cambrian or Devonian rocks are stratigraphic signatures of those ages. Accordingly, the Anthropocene signature is expressed by humanly affected changes in flora and fauna, as well as chemical changes resulting from human activities. The Sixth Extinction is the pattern of species extinction associated with human activity, although mass extinction isn’t the only signature of the Anthropocene.

My own view of Anthropocene signatures includes the extent of human transformation of the landscape, which becomes increasingly evident over time. Working at our Catskill site in the Hudson Valley, we were aware that the ridge to our east had been mined for Kalkberg chert and crystal-laden quartz thousands of years ago. Our 2019 excavation was finding evidence of the broad signature of this mining in the valley below the ridge, where we were digging up the Kalkberg chert and quartz crystals that Indigenous people had brought down to the bottom of an FTB fold. The bedrock at the bottom of the fold was from the next later limestone (i.e., New Scotland limestone) and did not contain chert (we established this by digging down to expose the bedrock, over and over again). Another ridge of Kalkberg limestone rises high to the west (I have the publications of geologists Stephen Marshak and Terry Engelder to thank for published maps and descriptions of this variation in stratigraphy and elevation). Without the fold-thrust situation, the New Scotland limestone would be above the Kalkberg. I assume with good reason that deeply down-folded Kalkberg limestone is below the New Scotland limestone in this valley.

Remarkably, during this work we found parts of an Onondaga limestone glacial erratic that had been taken apart to extract more chert. Intact erratics on nearby ridges often stand several feet high. This one was highly fragmentary, its post-demolition pieces buried in a shallow soil accumulation so there was no hint of its presence until some lucky archaeologists began to uncover it.

Glacial erratic with chert on a Catskill, NY ridge

Since last year, we finished a report on the human dimension of the Kalkberg chert, the quartz crystals, and the broken glacial erratic. Here, in the FTB, people removed choice parts of ridges in large quantities and manufactured useful things from them in the nearby valley, a little closer to water and in the warmth of south-facing slopes. Here they could practice their stone-craft with Old Sol rising behind the big ridge and passing pleasantly from east to west. Here and in other valleys next to rocky ridges in Greene County, New York, the dropped, lost, and discarded artifacts and lithic residue resulting from this activity have rather thoroughly infused the upper soil. It is no wonder that lately I contemplate how these hints of ancient stone industry seem to provide another signature of the Anthropocene, the latest epochal event in this old world’s history.

The Kalkberg chert-rich ridge towers in the background behind the excavators

References and further reading:

Curtin, Edward V.
2013 Phase 2 Archaeological Survey, The Birches at Schoharie, Route 30 (Main Street), Village of Schoharie, Schoharie County, New York. Curtin Archaeological Consulting, Inc., Ballston Spa, New York.

2015 Phase 1 Archaeological Survey, Catskill Exit 21 Development (Cat 21), Town of Catskill, Greene County, New York. Curtin Archaeological Consulting, Inc., Ballston Spa, New York.

2016 Phase 2 Archaeological Survey, Catskill Exit 21 Project, Route 23B, Town of Catskill, Greene County, New York. Curtin Archaeological Consulting, Inc., Ballston Spa, New York.

2017 Supplemental Phase 2 Archaeological Survey, Catskill Exit 21 Project, Route 23B, Town of Catskill, Greene County, New York. Curtin Archaeological Consulting, Inc., Ballston Spa, New York.

Curtin, Edward V. and Kirsten Dymond
2021 Phase 3 Data Recovery Project, Catskill Exit 21 Development Project, Site 1, Route 23B, Town of Catskill, Greene County, New York. Curtin Archaeological Consulting, Inc., Ballston Spa, New York.

DeSimone, David J.
2013 Geomorphology of the Fluvial Terrace at The Birches, Main Street, Schoharie, New York, DeSimone Geoscience Investigations, Inc., Petersburg, New York. In Phase 1B Archaeological Survey, The Birches at Schoharie, Route 30 (Main Street), Village of Schoharie, Schoharie County, New York. Curtin Archaeological Consulting, Inc., Ballston Spa, New York.

Gould, Stephen Jay
1987 Deep Time and Ceaseless Motion. In An Urchin in the Storm: Essays About Books and Ideas. W.W. Norton and Company, New York.

1989 Wonderful Life: The Burgess Shale and the Nature of History. W.W. Norton and Company, New York.

Isachsen, Y.W., E. Landing, J.M. Lauber, L.V. Rickard, and W.B. Rogers, editors
1991 Geology of New York: A Simplified Account. Educational Leaflet No, 28, New York State Museum, Albany.

Kolbert, Elizabeth
2014 The Sixth Extinction: An Unnatural History. Picador, Henry Holt and Company, New York.

Lindner, Christopher R.
1991 Archaeological Sites and Historical Floods in the Schoharie Valley, Eastern New York. The Hudson Valley Regional Review 8(2):104-138.

Majerczyk, Chris B.
2011 Geology of the Roberts Hill Area in the Hudson Valley Fold-Thrust Belt, Greene County, Eastern New York. Master’s Thesis in Geology, Graduate College of the University of Illinois, Urbana-Champagne.

Marshak, Stephen and Terry Engelder
1987 Exposures of the Hudson Valley Fold-Thrust Belt West of Catskill, New York. Geological Society of America Centennial Field Guide—Northeastern Section, 1987:123-128.

Marshak, Stephen, Kurtis C. Burmeister, Pragnyadipta Sen, Petr V. Yaklovlev, and Yvette D. Kuiper
2009 Structures of the Hudson-Valley Fold-Thrust Belt in the Appalachian Foreland of Eastern New York. NYSGA 2009 Trip 1.

McPhee, John
1981 Basin and Range. Farrar, Straus, and Giroux, New York.

1983 In Suspect Terrain. Farrar, Straus, and Giroux, New York.

Raymo, Chet and Maureen E. Raymo
2001 Written in Stone: A Geological History of the Northeastern United States, second edition. Black Dome, Hensonville, New York.