NOJSrOONTIi^UOUS SEDlxMENTATlON IN ICE CHANNELS. 401 



Gilbert and otliers have described a frontal glacial lake. At one time it 

 lay between the ice on the north and the hills on the south and overflowed 

 the Rome divide into the Mohawk Valley. A delta deposited by glacial 

 streams in this lake is found in Schroeppel, Oswego County, and extending 

 southward into Clay, Onondaga County, and other towns. Over most of 

 the Ontario slope in that region there are numerous short ridges and 

 mounds of glacial gravel, and some of them are arranged in north-and-south 

 lines, suggestive of deposition by a single glacial river. Is this association 

 of discontinuous deposits in the course of a single glacial stream, not only 

 on the coast of Maine but elsewhere, with the presence of a body of water 

 in front of the ice, causal or only accidental? 



Regarding the cases of discontinuous gravels in Maine at long distances 

 from the coast, the problem is complicated by the fact that in two or three 

 cases there were other causes that may have been more significant than the 

 presence of the frontal body of water. Thus, in Anson we are only 2 or 

 3 miles from a large terminal moraine, and the gravels may have formed 

 near the ice front as local kames rather than as parts of the original osar, 

 dating from a time when the ice of the Carrabassett Valley practically 

 formed a local glacier. The conditions in Abbott and Gruilford may be 

 very similar. 



The first question that arises in this discussion pertains to the effect of 

 the presence of the frontal body of water on the development of the sub- 

 glacial tunnels. We have seen that when the glacier lies partly below the 

 level of the frontal water, the tunnels and the connecting crevasses are jier- 

 manentl)'- filled with glacial waters up to the level of the sea or frontal lake. 

 The water in the crevasses would soon attain a temperature of 32° and then 

 float above the somewhat warmer water contained in the tunnels below 

 them. All the water of surface melting in this part of the glacier would 

 fall into the crevasses and become mixed with the water already occupying 

 the lower parts of the crevasses. The convection currents would be feeble, 

 and but little of the heat brought down by the surface waters would get 

 down into the subglacial tunnels and be available for enlarging them. 

 Only where the larger surface streams poured into crevasses would the 

 surface waters carry a surplus of heat into the subglacial tunnels. The 

 : smaller brooks and seeps would be so mixed with the cold waters of the cre- 

 vasses that their heat would be expended in melting the ice walls of the 

 HON xxxiv 1-'6 



