BEDROCK GEOLOGY
of the New York City
Catskill / Delaware Watersheds
Enlarged Version 525 X 360 (84Kb)

The Upper Devonian shale and sandstone bedrock shown in this map are underlain by a limestone layer that formed in a shallow marine environment. The next sedimentary rock layer was one of marine shale, followed by the terrestrial shales, sandstones, and conglomerates that crown the Catskill Mountains. The sedimentary deposits that formed these layers eroded from the once-great Acadian Mountains to the east. They washed into, and eventually displaced, a shallow inland sea, resulting in the formation of the "Catskill Delta". Millions of years of pressure and cementation turned these sea-floor deposits into our present-day bedrock. The bedrock present in the northeastern portion of the watershed is part of the Oneonta formation of the late Devonian Genesee group. This rock is composed of an array of conglomerate and cross-bedded sandstone steps, often divided by shaley inter-beds. These coarse-grained rocks are very resistant, capping the obvious escarpment that delineates the eastern and northeastern edges of the watershed.