Nature and Science: Geology
It’s all about rocks! Construction of the canal across New York was made possible thanks to the most significant gap in the Appalachian Mountain range. This low lying gap provided a natural avenue between the eastern seaboard and the Great Lakes through which a canal could be dug.
A shallow sea covered upstate New York during the period from 450 to 390 million years ago. Over time layers of shells and silt were deposited on the sea floor and were later compressed by overlying new sediments.
In this process, sand was solidified into sandstone, thick layers of mud became soft shales, and dissolved shells and calcium carbonate formed thin layers of resistant dolomite and limestone. In shallow bays, the seawater evaporated, leaving concentrations of dissolved minerals, such as salt and gypsum.
When the geologic events of the Alleghanian Orogeny, or mountain-building episode, thrust up the Appalachian Plateau during the period from 320 to 250 million years ago, the sedimentary rocks west of the Hudson were tipped gently to the south, exposing a cross section of layers. The tipped layers blocked the prevailing northward flow of water and redirected the streams into east-west channels that cut down into the softer layers.
The Mohawk, Seneca, and Clyde Rivers follow this east-west pattern, granting the Erie Canal an ease of construction and operation unknown to any other canal that attempted to unite the interior of the continent with the eastern seaboard.
As the streams cut down through the limestone caprock and tipped shale, they etched the surface into relief, leaving a pattern of steep slopes or escarpments facing north, and gentle slopes facing south. These escarpments extend east-west in bands across upstate New York. Along most of its length, the Erie Canal’s alignment took advantage of the east-west orientation of the underlying bedrock and the softer shales.
Crossing an escarpment, however, posed a major challenge, as evidenced in Lockport, where the Flight of Five locks climbs approximately 60 feet to ascend the Niagara Escarpment.
During the period from approximately one million to 10,000 years ago, successive waves of glaciers moved across the bedrock formation and shaped other distinctive landforms through processes of erosion and deposition. The glaciers also shaped many unique glacial features that form the characteristic landscape of upstate New York.