192 ROCHESTER ACADEMY OF SCIENCE. 



the mechanics of the process of esker formation according to the 

 superglacial view. 



ArguMient. The esker having come to rest upon the grovmd 

 will show the normal disregard for topography, its course being that 

 of the superglacial stream. 



Tributaries will be rare for aggradation will be confined to the 

 main channel for the most part by reason of the high gradient of 

 tributary channels. 



The general absence of eskers in mountain regions may be 

 explained because of excessive crevassing of ice not permitting the 

 extensive development of superglacial streams (66). Thus Hoist 

 explains their absence in south Greenland (66). In regions of 

 plains they are also apt to be absent because of the absence of large 

 drainage basins (66). 



Knolls are explained by the dumping of material into the main 

 superglacial valleys from hanging tributary valleys, by unevenness 

 in the surface upon which the esker ridge is deposited, and by irreg- 

 ularities induced by the gradual lowering of the esker deposit to the 

 base of the ice due to the unequal melting of the ice beneath the 

 esker. 



The widening of eskers toward their terminations is due to the 

 normal widening of the ice valley as it approaches a body of standing 

 water in which its walls are bathed, \^'ide places in the esker course, 

 the "plains", are due to the development of wide places in the super- 

 glacial valley. 



In case the esker channel is drained before subsidence is com- 

 pleted, the debris so left will protect the ice beneath from melting 

 and, becoming elevated on an ice ridge, will slide dow'u both sides 

 thus forming a double esker. 



The trend of eskers is in general conformity with the direction 

 of ice movements ; the slope of the upper surface of the ice is in 

 that direction so the esker streams naturally flowed in that direction. 



Reticulated eskers represent delta-like branching in broad 

 places in the superglacial channels, or a broad deposit split up into a 

 network of ridges while being let down upon the ground. 



The esker deposits may protect vast bodies of ice beneath from 

 melting after being aggregated into ridges by the superglacial 



