We are standing on a bridge that crosses a small creek entering Schoharie Reservoir. The creek has eroded down through quite a few layers of rock, allowing us to get a good look at them. These are sedimentary rocks of Devonian age that belong to the Unadilla Formation. The rocks around Oneonta are Unadilla Formation as well. These rocks contain ripple marks and cross-bedding that indicate deposition by streams and rivers. There are also some marine fossils preserved in these strata.
Here we must bear in mind a very important distinction!
Rivers play a key role here in two very different ways and at two very different times. 375 million years ago in the Devonian period rivers flowed here. These rivers were responsible for the deposition of the sediments upon which we are now standing, and formed the ripples and channels that we can see preserved in the rock. Schoharie Creek that flows here today is very different–it is much younger. This river came into existence after the glaciers melted 10 thousand years ago. This modern river is not depositing sediments, rather, it is eroding down through the ancient rocks of the Unadilla Formation. Schoharie Creek is cutting the small gorge in which we are standing.
Let’s walk down near Schoharie Creek
Here we see many sandstone beds that contain interesting primary structures. If we look down at the bed we are standing on we see that it contains numerous bits and pieces of wood. Just on the other side of Schoharie Reservoir are the fossil remains of the ancient Gilboa Tree Forest. These fossilized trees are 370 million years old. The wood fragments that we see here were probably derived from Gilboa trees.
As we walk toward the bridge we will examine the rock ledges closely. The rocks appear to be full of small, elongate holes. As we look more carefully we see that these are actually cavities formed by fossil shells. These shells belong to ancient marine creatures called brachiopods. Brachiopods look a lot like clams, and shared a similar lifestyle, however clams and brachiopods belong to different evolutionary groups of organisms.
We walk under the bridge and notice that the surfaces of the sandstone beds here are somewhat irregular, rather than flat. The layers form trough-shaped depressions or channels, and that is exactly what they are. The broad, U-shaped troughs were formed as small stream channels moves back and forth across the ancient land surface. The long-axis of the channel provides a clue to the direction that the streams were flowing–water flows parallel to the axis of the channel.
Climb back up toward the bridge (watch the poison ivy!). Near the road are outcrops with well-exposed cross-beds. These small cross-beds are further evidence that flowing water was responsible for the deposition of the sandstones here.
Finally–you may have noticed the “no trespassing” signs posted on trees as we walked to the creek and back. Schoharie reservoir and the land surrounding it belongs to the city of New York. Schoharie reservoir is one of the principle sources of drinking water for New York! Attempts by the city to regulate land use practices in Delaware county have caused considerable tension between the residents of “upstate” and “downstate.”
This year the residents of both New York city and the Catskills have to confront another water issue: drought. The summer of 1995 has been extremely dry, and reservoir levels have fallen dramatically. Some reservoirs are as low as 45% of their capacity.
Schoharie reservoir is clearly showing the effects of a summer without rain. The daily water allocation from the Catskill reservoirs to the city of New York has been reduced. For more information about the water shortage, click here.