GEOLOGY OF THE LAKE PLACID QUADRANGLE 99 



notch fault, whose displacements show little, if any, in the existing 

 topography, are probably much older, and they may in part at 

 least be of Precambrian age. Some of the fracturing is certainly 

 of later age than the diabase dikes because several of these in the 

 Lake Placid quadrangle have been crushed by the faulting. 



Cenozoic History 



The major existing relief features of the Lake Placid quadrangle 

 have been produced chiefly by the dissection of the upraised late 

 Mesozoic or early Cenozoic peneplain. As a result of the uplift 

 the streams were greatly revived as erosive agents, and they pro- 

 ceeded to carve out channels and valleys principally along the com- 

 paratively weak belts of Grenville rocks and the fault zones of 

 weakness. 



Late in the Cenozoic era the area of the quadrangle, in common 

 with most of the State, was deeply buried under the great ice 

 sheet of the Glacial epoch. ^ The continental, ice body in passing 

 across the quadrangle, in a south-southwesterly direction, removed 

 the residual soil of interglacial periods and subdued the contours 

 of the mountains. The tongues of the waning ice were influenced 

 by the topography, as is shown by the striae and the ice action in 

 the narrow valleys. In retreating from such valleys both ends were 

 blocked by moraines, usually forming basins between for the 

 accumulation of lakes. Many other, but more open, valleys were 

 dammed, producing lakes such as Lake Placid. The preglacial 

 stream valleys were likewise blocked and in some localities, as in 

 the case of the Ausable river near Keene, were forced to seek new 

 channels. 



The ice sheet left a mantle of till all over the area but much of 

 it has been washed into the valley bottoms where it was worked 

 over by the glacial lakes that were brought about by the ice 

 damming the normal drainage lines. Continuing after the with- 

 drawal of the ice body local glaciers persisted for a time on the 

 slopes of the higher mountains, as is indicated by the moraine in 

 the cirque on Esther mountain. 



It is the belief of the writer that the Lake Placid quadrangle 

 was situated near the northeast rim of the ring of ice that sur- 

 rounded and isolated the Adirondack highland from the rest of the 

 State during the retreat of the great ice sheet, and thus the north- 

 ward-draining valleys were blocked, preventing the escape of the 



^The summary of the Glacial and Postglacial history was written by Mr 

 H. L. Ailing. 



