Geological History and Structure main content.

Geological History and Structure

Part of Hall of New York State Environment.

Midway between the Hudson River and the Connecticut state line is the sharp profile of Stissing Mountain, 1,500 feet high and composed of modified granite called gneiss. Four types of rock are found at Pine Plains: gneiss, shale, limestone, and quartzite.

In the process of mountain-building the gneiss was raised with the sedimentary rocks (shale, limestone, and quartzite). Through millions of years the softer sedimentary rocks were worn away by erosion, leaving the hard core of Stissing. During this long period of erosion, red Triassic sandstones, which are still found in southern New York and the Connecticut Valley, probably covered the Stissing area. Such sandstones contain remains of dinosaurs and phytosaurs. In the recent period (perhaps within 10,000 years) mammoths and mastodons ranged at the edge of the retreating ice front. Their enormous teeth are occasionally found in the Pleistocene sands. Other interesting fossils are to be found in sedimentary rocks, especially those laid down in the ocean. By the presence of certain fossils the sequence and age of sedimentary beds can be determined.