Manhattan Island Geology | Gratacap: Geology of New York City Page 130



	106 GEOLOGY OF NEW YORK CITY Westchester County, both at Westchester and Eastchester villages and at Mott Haven, Morrisania, and Tremont, it is found, and is thence apparently divergently produced, being noted at Sing Sing, Sparta, Dobb's Ferry, Peekskill, Ver-planck's Point, Tarrytown, and White Plains. Professor Dana, in a series of elaborate observations, has undertaken to bring this Manhattan limestone into structural continuity with the Taconic marbles and schists, or that range of metamorphosed rocks which reaches northward through western New England. He would thus assign a Lower Silurian or Ordovician Age to the Kingsbridge rock. The evidence does not seem all exhausted yet, but there is a growing inclination, at least, to give these limestones a possibly lower place in the geological column than the rest of the



	island, making the Manhattan schists Hudson River. (Fig. 26.) The assumption that the limestone is later than the gneiss does seem, in a measure, controverted by the facts that first, the limestone in its southern prolongation at 3d and 4th Avenues and at 6th and 8th is so intermingled with the gneiss as to become itself schistose or laminated—a sort of gneissoid limestone—or, to read the inferences inversely, the gneiss has become so calcareous as to appear a limestone; and, secondly, the observation made by Stevens, and apparently repeated by Kemp, that at 3d and 4th Avenues the limestone is interbedded with two strata of gneiss, one above and one below ; and again by Stevens, that at 6th Avenue, in West i32d Street, the limestone is thrown upward in an arch with "the gneiss reposing conformably upon it," all of