THE LONG ISLAND COAST. 445 



Through this valley, probably much deeper than now, during the 

 period of elevation the Hudson flowed on its way to the ocean. Had 

 it been, as it now is, deeply submerged, no river could have flowed in 

 it, nor could it have been maintained as a valley while the deposit of 

 drift was going on. The facts imply elevation of the region to an 

 extent of from 300 to 400 feet above the present level of the sea. 

 This would change in a marked manner the aspect of the coast. The 

 site of the city of New York would be inland and greatly elevated, 

 while the gorges of the Hudson and East Rivers would be deepened 

 and widened by glacial torrents and ice. The ocean-border would be 

 from 70 to 80 miles southward from the present shore of Long Island, 

 and the deepest point attained in the artesian well on Barnum's Island 

 would be .above the level of the sea. 



There is reason to conclude that the entire subsidence of our coast, 

 from its greatest elevation in the glacial age to the greatest depres- 

 sion of the Champlain period which followed it, was from 600 to 700 

 feet, possibly much more than that. The elevation which followed 

 carried its stratified deposits not only to their present height above 

 tide, which, as we have seen, is about 260 feet, but at least 63 feet 

 more than that when the buried marsh at Fort Lafayette was formed 

 at the surface. By the present subsidence it is submerged or buried 

 to that depth. 



Here we pause. Further observations may confirm or correct our 

 conclusions. Geology has not a more tangled skein than is presented 

 in the structure of Long Island. There is evidence of minor oscilla- 

 tions, and pauses of movement, during which great clay deposits 

 formed in depressions upon the surface, now deeply covered with drift 

 or stratified sands, affording also some evidence that interglacial 

 periods, perhaps of mild climate, occurred, but more observations and 

 more facts ar.e needed to justify a definite judgment on the subject. 



Underneath the glacial drift, and underneath the sands which we 

 refer to the advent of the ice, are beds of clay and colored sands 

 which appear to be independent of the drift, and are referred to Ter- 

 tiary or Cretaceous periods. They appear at the surface along the 

 north side of the island, and are found buried by both unmodified 

 drift and by coarse glacial rubble. 



We present in tabular form the series of deposits which seem well 

 defined on Long Island, and which represent the probable order of 

 events, but they are fragmental, and perhaps do not occur anywhere 

 in a continuous vertical series : 



1. Shore and other surface formations. 



2. Stratified gravels and sands of the Champlain subsidence with fossil 

 shells of clam, oyster, and scallop ; also wood and lignite. 



3. Coarse glacial rubble in deep beds without fossils, representing floods at 

 the close of the Ice period, chiefly on the north side of the island. 



4. Unmodified bowlder-drift without fossils. 



