LONG ISLAND CLAYS. 115 



rock which occupied the site of Long Island Sound was the 

 crystalline dolomite which has been recognized as a metamorphic 

 limestone of Lower Silurian age. 



The inference from the facts presented and, indeed, the well- 

 founded conclusion, is that the portion of Long Island Sound 

 which borders Westchester County owes its origin in part to 

 the solution of a limestone which once occupied that place and 

 that the white and variegated clays of Long Island, some of 

 which have been regarded as of Cretaceous age on account of 

 the leaf prints contained in them, are accumulated residues from 

 the solution of that limestone under atmospheric agencies. 



How large a portion of Long Island Sound owes the forma- 

 tion of its depression to mechanical solution in the manner sug- 

 gested, cannot be determined in the light of present knowledge, 

 but it is probably safe to conclude that so far eastward as the 

 Palaeozoic rocks extend beyond the New York and Connecticut 

 boundary, these causes have had a controlling influence. 



The large granite area east of New Haven is regarded by 

 those who have given it most attention, as Precambrian, but 

 this is known to exist only along the northern margin of Long 

 Island Sound and it is entirely possible that to the south- 

 ward of these Precambrian rocks extended a large Palaeozoic 

 limestone area occupying the site of the present channel of the 

 Sound and which, by solution, has disappeared. 



We have at present no definite record of the occurrence of the 

 white and variegated clays oi) Long Island to the eastward of 

 Eaton's Neck where they are now found quite near the surface. 

 However, as they have been observed on Block Island and 

 Martha's Vineyard, it is possible that the deposit is continuous. 



