THE ADIRONDACK MOUNTAINS 6l 



directly across deep valleys, like that between Lake George village 

 and ^^'arrensburg, the rotten rock to a considerable depth may still 

 be seen in its original place. 



In conclusion we may say that, while many comparatively small 

 local features were produced by ice erosion, the major topography 

 of the Adirondacks was essentially unchanged by ice erosion. 



Local mountain glaciers. Certain mountainside valleys have 

 been notably modified by small so-called Alpine or valley glaciers 

 which existed either just prior to or just after the great Ice Age 

 in northern New York. On first thought it seems reasonable to 

 assume that such valley glaciers were lingering remnants of the 

 vast sheet of ice. But the absence of anything like distinct moraines 

 produced by such glaciers strongly argues for their existence just 

 before the Ice Age, such morainic deposits having been obliterated 

 by the passage of the great ice sheet. Excellent examples of valleys 

 once occupied and modified by local glaciers are the deep, nearly 

 U-shaped trenches down the eastern and northern sides of AMiite- 

 face mountain and down the northern end of the Sentinel range, 

 all within the Lake Placid quadrangle.^ 



Glacial deposits. The vast amount of debris transported by the 

 great ice sheet was carried either on its surface, or frozen within it 

 or pushed along under it. It was exceedingly heterogeneous material 

 ranging from the finest clay, through sand and gravel, to boulders of 

 many tons weight. The deposition of these materials as we now see 

 them took place during both the advance and the retreat of the ice, 

 but chiefly during the retreat. Most of the deposits made during 

 the ice advance were obliterated by ice erosion, but those formed 

 during the ice retreat have been left intact except for the small 

 .amount of postglacial erosion. 



A\"henever, during the great general retreat, the ice front remained 

 stationary for some time because the forward motion of the ice was 

 just counterbalanced by the melting, all the ice reaching the margin 

 • dropped its load of debris to build up a terminal moraine. This is 

 usually a distinct ridge of low hills consisting of very heterogeneous. 

 : mostly unstratified, debris. Such moraines are not commonly well 

 developed in the Adirondacks. 



A very extensive glacial deposit, called the ground moraine, is 

 simplv the heterogeneous, typically unstratified debris from the 

 bottom of the ice which was deposited mostly during the melting 

 and retreat of the ice. When it is mostlv verv fine material with 



1 Prof. D. W. Johnson has recently noted a moraine in one of the val- 

 leys of Mt. Whiteface and he argues that it was produced by a local glacier 

 which existed after the retreat of the great ice sheet. 



