40 NEW YORK STATE MUSEUM 



The full significance of the glacial deposits of the Remsen quad- 

 rangle will not be known until careful work has been done in the 

 contiguous areas and in fact along the whole Mohawk valley. 

 The writings of Chamberlin,^ Brigham ^ and Gushing ^ are here 

 referred to as bearing directly upon the subject. Brigham, whose 

 work is particularly noteworthy, is now engaged in further study 

 of this problem. The discussion here presented is decidedly local 

 in its character, the purpose bein^ merely to record certain observa- 

 tions and to offer some suggestions which bear upon the broader 

 problem. 



Ice erosion 



As the ice slowly moved across the country the preglacial rock 

 surface was more or less scratched and eroded, but there is no good 

 reason for thinking that the old rock surface w^as profoundly 

 affected in this way. In the western part of the district, and 

 extending out for a considerable distance from the shale area the 

 heavy crystalline beds of the upper Trenton nearly always make 

 up the surface rock formation and no isolated shale masses can be 

 found. The shale rises rather abruptly above the limestone area 

 culminating in the high land around Starr hill. The writer inclines 

 to the belief that immediately before the advent of the ice, thin 

 shale masses extended farther eastward over the limestone. Cer- 

 tain it is that at one time the shale did thus extend out and that 

 it has been removed either by water erosion or by ice erosion. 

 As the ice moved across the country the tendency w^ould be for 

 the softer shales to be more easily removed than the more resistant 

 heavy beds of limestone. Both types of erosion should be con- 

 sidered and no doubt the stripping off action of the ice was im- 

 portant. Among the evidences favoring this view are : the presence 

 of the thin mass of coarse crystalline limestone over such a wide 

 area; the greater resistance to erosion of the limestone; the preva- 

 lence of glacial till full of shale fragments and directly overlying the 

 limestone. 



Direction of ice movement 



Chamberlin, in the report above referred to, makes the tentative 

 statement " that strong ice currents swept around the Adirondacks 

 and entered the Mohawk valley at either extremity, while a feebler 

 current, at the hight of glaciation probably passed over the Adiron- 

 dacks and gave to the whole a southerly trend." Observations 

 by later investigators have tended to bear out this view. This con- 



» U. S. Geol. Sur. 3d An. Rep't., p. 361-65. 

 ' Geol. Soc. Am. Bui. o, p. 183-210. 

 » N. Y. State Mus. Bui. 77, p. 73-81. 



