An Ancient Ocean and Mountain Chain

Notice the alternating layers of blocky sandstone and thinner, flaky layers of shale of the gorge walls. These sedimentary rocks were formed during the Devonian Period, 410 – 360 million years ago, when a shallow, inland ocean covered much of what is now New York State. Streams flowing down a vast mountain chain into this ocean deposited sediments of sand, gravel, and mud, which accumulated over millions of years to form these thick stacks of sedimentary rocks. Over time, the shifting of continental plates reloacted this bedrock from around the equator to its present-day location.