A Catskill Catalog: Sept. 9, 2009
I am just about the last guy to try to explain the geology of the Catskills. I failed high school physics. Never took earth science.
Fortunately, our mountains have our own geologist, Bob Titus, professor of geology at Oneonta’s Hartwick College, who lectures regularly on Catskill Mountain geology. Unfortunately, I’ve never heard him lecture. And even a bit of scientific reading somehow makes my eyes glaze over. I say this both as confession and warning. I’m not the guy to do this. But a full catalog requires it. So here goes.
According to Bradford Van Diver’s geology field guide Upstate New York (Kendell/Hunt publishing Co., Dubuque, Iowa, 1980), the geologic framework of upstate is comprised of six “physiographic provinces,” regions “with a certain topographic ‘personality,” such as mountain, valley, or plateau.”
The Catskills are wholly contained in the province termed Appalachian Uplands, which extends along the southern tier of the state south of the Portage Escarpment, an east-west series of highland cliff-edges that rise from the central lowlands south of Lake Ontario and the Mohawk River Valley. The dramatic northeast boundary of the Appalachian Uplands is the Helderberg Escarpment. The overlooks at Albany County’s Thatcher Park make clear this geologic boundary in the spectacular views of the lowlands extending northward from the ledge.
The southeastern corner of this Appalachian Upland is the Shawangunk Ridge down by New Paltz. While the book doesn’t say so, it’s clear that part of the eastern boundary is the Great Wall of Manitou, the escarpment at the edge of the mountaintop over past Windham, the cliff-edge at North-South Lake, up in Haines Falls, where the old Catskill Mountain House once stood.
Sedimentary rock forms the bedrock of nearly the entire Appalachian Upland in the state. Geologists call the bedrock floor the Catskill Delta. Evidently, about 395 million years ago, the prehistoric Acadian Mountains rose in the New England region, sending a lot of run-off this way, forming a spreading wedge of wash that evolved into a shallow inland sea. This delta formed the bedrock.
Perhaps, that inland sea explains the smooth stones I once found at the top of Slide Mountain, stones very much like the beach stones I like to pick up at the seashore. Always wondered about that.
In the Catskills, the Catskill Delta bedrock runs 7,500 feet thick. “Downstream,” near Lake Erie, it’s more like 2,000 feet thick. The bedrock here used to be a lot thicker, but erosion wore a lot of rock away.
That’s what folks mean when they say the Catskills are a dissected plateau. The Great Devonian sea era had already uplifted the land. Then millions of years of runoff and erosion dissected that upland plateau into sharp contrasts of elevation. Doesn’t mean the Catskills aren’t mountains. Means our mountains were formed by the movement of water and ice. At least, I think that’s what it means.
The rock itself is primarily shale. The bedrock closest to the surface is comprised of red and green shale, sandstone, and conglomerates, rock that indicates a prehistoric shoreline environment. Below that, the shales, siltstones, and sandstones move from grey to black revealing the depths of that long-gone inland sea.
The Devonian period of geologic time – 345 to 395 million years ago – corresponds with the Paleozoic Era, the great era of fossil creation, so the shales and sandstones of the region have been an important source of fossil remains.
Cool autumnal air invites a mountain ride. Consider a trip to Gilboa to see the roadside display on the famous Gilboa fossils. In 1850, an amateur rock scientist found a fossilized tree trunk in the creek after a flash flood. Turned out to be 380 million years old, evidence of the oldest forest on the globe. Further digs found more fossils of trees and vegetation.
What is exciting about this is the age. The Gilboa fossils are from the time when this part of the earth was moving from an entirely marine, underwater world, to one that was terrestrial and grounded. These might be the world’s first trees!
I know I like to make big claims for the Catskills but this is ridiculous.
Twenty thousand years ago, all of New York State was covered in glacier; ice more than a mile thick in some places. The glacier was a major factor in the plateau dissecting that gave us the Catskills. Evidence of glacial advance is still visible. Over near Roxbury, along the cut-off road that runs between Route 30 and West Settlement, on the way to the old Bellevue Lumber, is a hump-like rise of land that is a glacial moraine, a “ridge of till left at the glacier front at its farthest advance.” My friend Joe once pointed that out to me.
Geology is pretty interesting. I oughta take a course.