The Geology of New York State: A Brief Summary

Starting around 500 million years ago, the two land masses that were roughly equivalent to what are today Europe and North America began collide with one another. These collisions of landmasses pushed up a range of very high mountains along the margin of North America. Today we call the remnants of those mountains the Appalachians, and they extend from eastern Canada to Alabama. Four hundred million years ago they were much higher than they are today, perhaps as high as the Himalayas are now.

For several hundred million years, global sea level was sufficiently high and the land surface west of the mountains was sufficiently low for the ocean to "flood" the region. This created a broad shallow sea covering part of the continent. At certain times (especially during the Silurian period, 440-415 million years ago), this sea was very shallow indeed, and evaporation of seawater formed thick salt deposits that are mined today across central New York. Around 410 million years ago, sea levels rose. The area that is now the northeastern United States, including New York, was near the equator, and the oceans were warm and tropical. Marine life thrived on the sea bottom, and the skeletons of these marine organisms piled up on the seafloor. Some of these skeletons were made of calcium carbonate, which formed lime mud that eventually became limestone.

This glass sponge (Uphantaenia chemungensis) is an example of the ancient marine life that existed in the Upper Devonian period. Found near Spencer, NY, it is part of PRI's vast fossil collections.

As the high mountains to the east of this sea continued to erode, huge quantities of gravel, sand, and mud flowed off the land into the shallow sea. These sediments formed the thick stack of sedimentary rocks of Devonian age across much of central New York State. The coarse-grained sediments piled up in deltas and beaches close to land, forming sandstones. The fine-grained sediments stayed suspended in water longer and moved westward farther out to sea toward the west. They piled up in deeper, quieter waters and formed siltstone and shale.

The blackest mud accumulated in water that contained little or no oxygen (and so the black carbon in the mud did not oxidize); this mud today forms the great thicknesses of black shales throughout much of central New York.

By the end of the Devonian Period (360 million years ago), as deltas from the mountains built out into central New York and as global sea levels fell, the shallow seas began to retreat from the northeastern U.S. The sea continued to exist for a time in other parts of the continental United States; the great coal beds of Pennsylvania result from coastal forests that covered this area during the Carboniferous Period, immediately after the Devonian. By the start of the age of dinosaurs around 240 million years ago, the region was dry land. Although dinosaurs left their footprints in the red sandstones of the Connecticut River Valley of Massachusetts and Connecticut, barely a trace of them remains in New York. Only a single set of fossil footprints is known from near Nyack, in Rockland County. This is because most rocks of Mesozoic age (240 - 65 million years ago, when the dinosaurs lived) have been removed by erosion.

There were, however, almost surely dinosaurs wandering through central New York for many millions of years. Possibly the area was flooded by seawater again during the Cretaceous Period, about 100 million years ago, during which time great marine reptiles and sea life would have thrived. The sea would have receded again by the end of the age of dinosaurs, and probably great mammals (animals with fur) occupied the landscape over the past 60 million years. But these events are not recorded in central New York, because sediments and fossils within them have been long erased, weathered and eroded by winds and rain, freezing and thawing, and finally the bulldozing of sheets of ice. This erosion has even erased the uppermost rocks from the Devonian Period.

The next recorded chapter of the geological history of New York State is the Ice Age, which began approximately two million years ago, and left the lakes, gorges, and gravel of the Finger Lakes region and elsewhere behind as a reminder. In the landforms and glacial gravel we can find a record of how the glaciers moved, and sometimes find the bones of animals that lived along the margin of the great sheets of ice.

Cecil, PRI's mascot for the new Museum of the Earth, is a dinosaur called a Coelophysis. Coelophysis trackways are among the few dinosaurs fossils that have been found in New York State.