54 NEW YORK STATE MUSEUM 



between the clearly recognizable Wisconsin drift and the ancient 

 Paleozoic rocks. These clays are evidently nonglacial, but whether 

 they are Pleistocene or not is undetermined. The clays contain 

 Potsdam pebbles up to 3 inches in diameter, of angular shapes and 

 free from striae of any sort. Floating ice appears to be demanded 

 for the distribution of such pebbles in stratified clays, and it is 

 possible that the deposit is Pleistocene in age. The top of these 

 clays is approximately 400 feet above the present sea level. 



The principal surficial glacial deposits of the region pertain 

 to the latest stages of the ice sheet and were formed at a time 

 when the country to the southward was free from ice.. They are 

 undoubtedly contemporaneous with many of the deltas and lake 

 beaches about the southern borders of the Adirondacks, and 

 with the water levels in the upper Hudson valley. 



As the ice front receded from the foothills of the Adirondacks, 

 recessional frontal moraines were formed, and, when the ice had 

 receded far enough to permit of the existence of northward flowing 

 streams having a considerable volume of water, this drainage 

 as well as that from the ice became organized in torrential 

 streams, escaping along the ice margin toward the east into 

 a glacial lake covering the site of the present Lake Champlain. 

 These waters flowed across the " flat rock " or spillway at " the 

 Gulf" on the international boundary. As the ice retreated, but 

 before it retreated from the north slope of Covey hill, it seems to 

 have opened a passage just north of the boundary and east of " the 

 Gulf," so that the waters passing through " the Gulf " for 

 a time entered a glacial lake near the mouth of " the Gulf." 

 Eventually the ice melted out from the St Lawrence valley so 

 as to permit the ingress of sea water, whereon strong wave 

 action took place at what is now an elevation of 450 feet on 

 the north slope of Covey hill. Southward wave action is found 

 above and below this limit. That above is referred to a glacial 

 lake, that below mainly to the sea. On the Plattsburg quadrangle, 

 to the southward, there is a cliff with strong delta building at 

 about 330 feet, phenomena which are taken to mark the marine 

 limit at that place. The marine limit fixed in this manner is inter- 

 preted to indicate a rise of the old sea level on the north at the 

 rate of 4.41 feet to the mile. This would place the marine limit on 



