GEOLOGY OF MOUNT MARCY 9 



The ice sheet freshened up cHffs, removed the weathered and loose 

 mantle of debris, and filled the depressions with drift. Upon this 

 the postglacial streams have established themselves undoubtedly 

 following for the most part the old preglacial lines. This topic will 

 be more fully discussed under Pleistocene geology. 



In the southeastern corner of the quadrangle the brooks manifest 

 in an appreciable degree the " trellised drainage " which is much 

 better shown in the neighboring Elizabethtown quadrangle. 



Lakes. The quadrangle is not rich in lakes as judged by the gen- 

 eral standards of Adirondack areas. Yet several of the bodies of 

 water present features of great scenic beauty and of much geologic 

 interest. 



The best known are the Ausable lakes, a divided pair of long, 

 narrow character, practically forming the source of the East branch 

 of the Ausable river. They lie in a contracted fault valley with 

 steep rocky sides. The valley is essentially a unit, but the lakes 

 are separated by a mile of sand and gravel, obviously the alluvial 

 fan and delta which Shanty brook has poured into the depression 

 so as to separate into two what was originally one. The dividing 

 flat of gravel and sand may have some foundation of morainal mate- 

 rials, not now visible, but its most probable explanation is the rapid 

 deposition of drift washed in by Shanty brook soon after the 

 departure of the ice sheet and modified and leveled off by periods of 

 high water in the two ponds. The flat acts as a dam for the upper 

 lake, which stands over 30 feet higher than the lower one (see 

 frontispiece). 



The relationships are somewhat similar in the Cascade lakes, 

 formerly called Edwards ponds and still earlier Long pond. They 

 lie in a long, narrow, fault valley, with precipitous rocky sides. 

 They owe their twofold character to a mass of boulders, gravel 

 and sand and are believed to be due to an avalanche in 1830. The 

 materials have come from the mountain on the south side and hold 

 the western lake about 7 feet higher than its mate. The barrier 

 of the eastern lake is a mass of boulders and sand, reinforced by 

 vegetation, as is shown in plate 5. 



Avalanche lake lies in a narrow fault valley along the eastern 

 front of Mount Maclntyre. Its banks are so precipitous as to require 

 a scramble for their passage. Like the other cases just cited, its 

 waters are ponded back by a barrier of drift. 



Chapel pond on the road to the southeast from Beedes (Ausable 

 Club) is a very interesting case of a body of water confined by a 



