The ice sheet, when it came down over this area, scoured the rocks, removing all soil. As the ice front receded (about 15,000 years ago) it left behind stranded ice blocks, glacial lakes, and a thin mantle of rock fragments and powder. Along its margin the highest mountains, or nunataks, projected above the ice.
Triassic Red Sandstone Slabs
Triassic Red Sandstone Slab (from East Paterson, New Jersey), polished and striated by the moving ice sheet.
The striae, or parallel scratches, were scraped by rock fragments in the ice. The boulders, carried along by the ice, were found in the same locality.
Above is a later stage of the glacial retreat in which appear vegetation and mastodons which are now extinct. The hill-like residues are kames; the long ridges formed by estream tunnels beneath the ice are eskers. No special locality is represented, but similar glacial conditions are still to be found along the Greenland coast.
Part of Hall of New York State Environment.