[J. Thomas Scharf (1886)] Most of them are fragments of our own rock-beds, while many are of foreign ma-' terial, having found their way here during the drift I period, of which they are not the only remaining evidence. The surface of most of our rocks are well polished and furrowed by the same agency. There are several places in the town where the dolomitic limestone, which exists in several localities jl in Westchester County, crops out; but it is only, quarried to any considerable extent on the New York. j State Prison grounds. It is a species of marble, and hears the name of the locality from w hich it is taken, || as the Sing Sing, or Pleasantville, or Kastehester J I marble. It differs from common marble in being a,, I bibasic mineral. Ordinary marble is a simple car-j OSSINTNG. 323 bonate of lime, while this is a carbonate of lime and;i carbonate of magnesium. It is, for the most part, granular and readily disintegrates by exposure to at-mospheric influences. It is this quality that renders it unsuitable as a building stone for permanent struc-tures. Much of this marble, however, is very com-pact, crystalline and solid, making an excellent build-ing material, and has heretofore been largely employed for this purpose, f The extensive buildings erected by the State, for / the prisons and shops at Sing Sing, including the large Doric structure formerly used as a prison for fe-male convicts, were all made from these quarries.