96. Irondequoit Limestone

The Irondequoit Limestone is a fossil-rich, geologic rock formation of Silurian age. It outcrops extensively along the Niagara Escarpment in western New York and southern Ontario, and provides a vital marker bed that geologists use to understand the ancient aquatic ecosystems and landscape evolution of the region. 

The Irondequoit is a mapped unit of Limestone with outcrops in western New York, and Ontario. It is a member of the Clinton Group. Subsurface it extends into northern Pennsylvania.[1] The Irondequoit is described as a light gray-pinkish gray limestone-greenish gray carbonate. It tends to have abundant crinoids and brachiopods with some rugosa corals bound into a grainstone or packstone in the west.[2][1] The beds are thick to massive. Toward the top of the formation as it nears the Rochester Formation thin greenish gray bed of shale maybe present. Reef knolls have been observed in the upper sections of the formation ranging from three to ten feet wide and up to six and a half feet tall. In the east it grades to packstones to wackestones.

About a mile down the railroad tracks going NE you move down back into the lower Irodequoit Limestone which seems harder (more dolomitic) and then it turns into the Grimsby Sandstone.