The Lockport Formation in New York extends from Niagara Falls 200 mi eastward to Ilion Gorge where it pinches out. Within the Lockport vertical and lateral lithologic differences permit recognition of members. At Niagara Falls the formation is 200 ft thick and consists of 5 dolomite members, in ascending order, the Decew, Gasport, Goat Island, Eramosa, and Oak Orchard. Farther E. at Rochester, the Lockport comprises the DeCew, Penfield (new name), and Oak Orchard members. From the Clyde to Oneida quadrangles, the limestone and dolomite facies are placed in a new member, the Sconondoa. The eastward-thinning Ilion Member of shale and dolomite occurs in the Rome, Utica, and Winfield quadrangles. E. of the Winfield quadrangle the Lockport is absent but its stratigraphic position is believed to be occupied in part by the upper Herkimer Sandstone (Clinton) and in part by the Herkimer-Brayman (Salina) disconformity.