the ice sheet still covered the present Clark Reservation. The threshold for water to flow through this channel is at above sea level. As the ice sheet retreated, the waters found a new, lower channel running through Clark Reservation, with a channel threshold of about . A waterfall formed, and its plunge pool ultimately became Glacier Lake. As the ice retreated further northward, a still lower channel (Rock-cut channel) was carved where Interstate 481 is currently located (channel threshold of about ). The channels at Pumpkin Hollow, Meadowbrook, and at Green Lakes State Park have the same origins. Roseberry writes, "The abandoned gorges indicate a complex series of glacial rivers parallel to the receding ice front, producing waterfalls when they dropped over north-south ridges." The relief of the fossil waterfall at Clark Reservation is somewhat larger than that of Niagara Falls (). As at Niagara Falls, the well defined falls occurred because of the presence of a capstone layer of limestone that was resistant to erosion by the flowing river. Roseberry writes that this "limestone is deeply waterworn and fissured, mutely telling the force of the deluge which hurled itself over the brink." The limestone shelf leading to the precipice at Clark Reservation is an example of a "karst" topography created by water's dissolution of limestone and related rocks. Among its features is a deep depression in the limestone that is known as Dry Lake. Dry Lake is about deep and occupies , and offers an unusual habitat for plants. As Franco, et al. report, "It is believed to be a karst feature created by dissolving limestone that formed a sinkhole basin. The bedrock is 300–400 million years old (Van Diver 1985) and its fissures allowed for rapid post-glacial water drainage." See also List of New York state parks References External links Website of a private, non-profit, volunteer organization that supports Clark Reservation. Photograph of American hart's tongue fern. State parks of New York (state) Meromictic lakes Nature centers in New York (state) Parks in Onondaga County, New York DeWitt, New York