622 NKW YORK STATE MUSEUM 



The fact that, wlierever these older chiys are now seen in the cliffs 

 and ex]H>6ures ahont the north shore of Lon^^ Island, tliey are 

 involved in folds and distnrbances witli the earlier i^lacial gravels 

 and sands is evidence that thev have been disturbed dnrino: Pleisto- 

 cene time by the same agency which j)rodnced disl<>cations in the 

 earlier glacial dej>osits. Since they have been thus dis})laced, their 

 present relief cixn not be taken as evidence of tiie form of the land 

 surface on which the glacial deposits were laid down. It is even 

 uncertain whether the de})ression known as Long Island sound had 

 any existence prior to tiie disturbances in which these clays were 

 involved in Pleistocene time. Everywhere the existing relief of 

 these clay masses above sealevel is a function of their displacement. 

 The entire absence of anv relativelv hard or resistant lavcr iu the 

 series makes it even doubtful if the seaward migrating outcrops of. 

 the Cretaceous series presented at the time of the first ice invasion, 

 anywhere along the line from Cape Cod or Nantucket westward to 

 New Jersey, anything like a bluff or inface of strata overlooking the 

 bared, hard rock terrane on the north, such as might be expected 

 were the rocks of a firmer character or of greater lithulogic variety. 

 At most, where these older clays now rise highest in dislocated 

 masses, it may be that remnants of the old coastal plain, similar in 

 origin to the highlands of Xavesink on the New Jei*sey coast, stood 

 up on the interstream areas. The deep reentrants of the northern 

 coast, as in the case of Hempstead bay, apjiear to be features of 

 Pleistocene date, across whose site the Cretaceous clays previously 

 extended unbroken. In short, no definite trace of an older detail of 

 land surface is now discernible beneath the glacial materials within 

 the limits of thie report. The absence, however, of deposits inter- 

 mediate in date between the older Pleistocene and the ancient clays 

 warrants the supposition that at least the northern part of the island 

 was an area of erosion by ordinary meteoric agencies. 



Iteneath the Cretaceous and Potomac clays should come the hard 

 rcxsks exposed on the maiidand. These hard rocks in the form of 

 gneiss appear at the surface westward in Long Island City an<l 

 have Ixfen met in lj<jrings in Brooklyn. The precise depth at which 

 they occur l>eneath this area is at present a matter of conjecture. 



The entire absence of hard rocks in fixed ledges or outcrops within 



