Geology of Long Island. 345 



clay streaked with limonite occurs?, intercalated with the till. 

 At the end of the point, a similar bed of clay is exposed, over- 

 lain by stratified sand. From the extremely limited character 

 of the exposures, I am unable to determine whether the clay un- 

 derlies the whole of the point or is merely local in its occurrence. 

 In character and position, however, it is analogous to beds occur- 

 ring on Block Island. 



The boulders of Long Island attract the attention of the geol- 

 ogist by their size and variety. They represent almost every 

 geological age ; fossiliferous rocks of the Helderberg, Oriskany 

 and Cauda Galli, Hamilton, Chemung and Eocene periods having 

 been found in the drift. Examples of these are in the collection 

 of the Long Island Historical Society. There are also various 

 members of the Archaean series, viz., gneiss, granite, syenite, 

 hornblende, chlorite, talcose and mica schist, limestone, dolo- 

 mite, and serpentine ; and the Palaeozoic and Mesozoic ages are 

 represented by Potsdam sandstone, Hudson River slate, Oneida 

 conglomerate or Shawangunk grit, Catskill sandstone, and Tri- 

 assic sandstone and trap. As the lithology of the boulders has 

 been described in detail by Mather,* it would be superfluous for 

 me to undertake a similar description. 



In addition to the rocks mentioned above, a ferruginous sand- 

 stone and conglomerate occur abundantly in fragments along the 

 east shore of Hempstead Harbor, and in the drift between Glen 

 Cove and Oyster Bay. Many of these fragments contain vegeta- 

 ble impressions, but in only two localities have any leaf prints 

 been found. These were West Island, Dosoris, and the well of 

 the Williamsburg Gas Co. The prints are supposed to belong 

 to Cretaceous plants, but the evidence is incomplete. 



Many of the erratic blocks are of immense size, one in particu- 

 lar, of gneiss, on Shelter Island, near Jennings' Point, con- 

 tained as a solid mass over 9000 cubic feet. It has split in three 

 pieces since it was deposited. Matherf mentions a mass of gra- 

 nite near Plandome, which was estimated to contain 8000 cubic 

 yards above the surface of the ground. 



Having thus briefly reviewed the characters of the surface 



* Geol. 1st Dist, N. Y., pp. 165-177. 

 f Geol. 1st Dist., p. 174. 



