HILLSIDE OSAES OR ESKERS. 367 



2. That subglacial streams flowed up and over the hills. North of all 

 hills there is always a portion of a subglacial stream tunnel where the water 

 is in equilibrium to the top of the hill and flows only as it is urged by 

 water from behind rising above the top of the hill. If the tunnel were 

 rather large for the supply of water, the flow up the hill might be so slow 

 that it would not erode channels in the ground moraine and the only gla- 

 cial sediments would be deposited in the valley to the northward. I have 

 found no such sediments as yet. Or the streams may have been too small 

 to transport noticeable masses of gravels. 



Superficial streams flowing from the north might at or near the tops 

 and southern brows of the hills pour down the crevasses that would natu- 

 rally form there and escape down the slopes as subglacial streams, or they 

 might continue in superficial channels, in which, after they had cut down 

 to the bottom of the ice, the gravels were deposited. But all observation 

 proves that on these steep hill slopes the ice would almost certainly be 

 deeply shattered by crevasses, and hence it is extremely unlikely that the 

 channels were superficial on the hillsides. The esker or kame, elsewhere 

 described in Jay, contains so large bowlderets and bowlders that it becomes 

 probable that this kame was deposited in subglacial vaults. The plexus of 

 reticulated ridges can be accounted for on either the theory of subglacial 

 or superglacial streams. Where the terminal enlargement takes the form 

 of a horizontally stratified delta, the stream evidentlj^ escaped into a pool 

 within the ice, or where the delta spreads out in the valley and jDasses by 

 degrees into the valley drift, the stream passed beyond the ice into the open 

 valley. In this case it is doubtful if the delta furnished the evidence neces- 

 sary to decide definitely the question of the nature of the streams. 



The hillside eskers were perhaps not all deposited in the same manner. 

 They are in situations so favorable to the production of crevasses that it 

 would appear to be inevitable that a part, if not all, were formed by 

 streams which, no matter what was their history toward the north, escaped 

 down the hills as subglacial streams. On this liypothesis the shortness of 

 the ridges would be accounted for partly by the fact that the water would 

 cease to flow from the north as soon as the melting had progressed so that 

 the hills emerged from the ice. Some of these kames seem to prove that 

 the flow continued long enough to permit the formation of subglacial tun- 

 nels in places where there had been none until the ice became quite 

 thin. These subglacial channels were not prolonged far. 



