ICE-SHEET EROSION IN NEW YORK 59 



higher ground either side of the valley, but they are chiefly due to the 

 relatively slower melting of the deeper portions of the front. 



Effect of deep waters facing the ice.— Probably during the advance of 

 the ice sheet, and certainly during its retreat, all the valley lobes were 

 fronted by deep glacial lakes. It has been questioned whether the val- 

 leys did not have reentrants in the ice front instead of lobations. In 

 any case, the water was unfavorable to elongation of the lobes, due to its 

 melting effect, and unfavorable to ice erosion on account of its buoyant 

 effect. The earlier glacial waters had a depth in both Cayuga and Seneca 

 olf over 1,000 feet, while the Warren waters, during the withdrawal of the 

 ice from the valleys, had a depth of over 800 feet in Cayuga and greater 

 in Seneca. 



The detrital deposits left in the waters which faced the retreating ice 

 give no evidence of having been formed along the margin of ice tongues, 

 and the drainage lines down the valley walls show no diversion due to 

 ice occupation. 



Whatever was the kind and amount of work by the ice in the Finger 

 Lakes region, it was only that of a continental ice sheet and not that of 

 stream or alpine glaciers. 



No erosion in front of zone of deposition. — The existence north of the 

 lakes of the ground moraine valley-filling crowned with drumlins has 

 been referred to above. Perhaps one might regard this deposit as an 

 early terminal moraine overridden by later ice advance. Certainly it is 

 not terminal drift of glacial recession. But, whatever the view as to its 

 origin, it proves the transportational impotency of the ice along that 

 zone, and it is unreasonable to suppose that the lower ice, on a rising 

 slope, could effectively erode in front of this zone of deposition. 



It therefore seems impossible that the ice body which left the drumlin 

 belt filling could have eroded the Finger Lakes basins. Of any earlier 

 and more powerful invasion than that of the Wisconsin ice sheet we 

 have no evidence whatever in this region. 



Absence of moraines in the basins. — There are no conspicuous mo- 

 raines in the Seneca or Cayuga valleys between the heavy deposits 

 left at the receding front, which now form the valley heads, and that 

 which carries the drumlins and constitutes the blockade on the north. 

 There are no pronounced valley moraines except at the valley heads. 

 For some 50 miles, the stretch between the two deposits named, the val- 

 ley walls are comparatively free from localized drift. This absence of 

 recessional moraines is a surprising and important fact. Some accumu- 

 lations may be covered by the deep lakes; but surveys do not reveal 

 them, and the lakeless valleys and those with only shallow lakes are also 

 characterized by general absence of valley drift and the smoothness of 



