332 GLACIAL GRAVELS OF MAINE. 



the end of the ice. Such matter would be less rolled. Where the ice 

 met the sea a marine delta would be formed in front of it. Where the 

 ice front was above the sea, as was probably the case for a time in the 

 valleys of the Carrabassett and several other streams at about the same 

 distance from the coast, plains of gravel were formed in the valleys in 

 front of the ice. With respect to the glacial streams and the ice front, these 

 may be termed frontal deltas or overwash ajjrons. They are the correlative 

 of the sediments formed in front of all glaciers ending on the land. Such 

 a series of frontal plains were found south of the great terminal inoraines 

 of the ice-sheet for a considerable part of their length. At the south end 

 of Sebago Lake a very deep mass of glacial gravel accumulated, and, as 

 elsewhere explained, ice movements ' probably contributed , to bring this 

 great mass together, although it must be admitted that glacial streams can 

 transport sediments long distances. 



(b) When the flow of a subglacial stream was transverse to that of 

 the ice. The great size of the stones and bowlders contained in the gravels 

 of the hilly country west of the Saco River, and other facts, favor the 

 hypothesis that they were deposited in large part by subglacial streams. 

 If so, the eskers must often have been deposited in such subglacial 

 channels transversely to the flow of ice, for the ridges of those reticulated 

 series of kames trend in every direction. In this case either (1) the ice 

 pushed the channel with its contained sediments bodily forward, or (2) the 

 ice flowed over the gravel, or (3) the ice was melted and eroded by the 

 stream as fast as it advanced, or (4) the ice may sometimes have been 

 stationary. The truth probably coml^ines the second and third hypotheses, 

 and in both cases some morainal matter would he dropped into the channel 

 as the ice passed over it. 



(c) When the channel was j^arallel with the direction of ice flow. In 

 this case it is certain that there would, especially in case of deep ice, be 

 more or less flow of the ice inward from the sides. That the channel did 

 not then collapse, like an unused moulin shaft, must be due to the antago- 

 nistic action of the stream enlarging its channel. Some till would be con- 

 tained within the ice melted and eroded as it flowed inward, and thus some 

 esker matter would be brought together. 



(f^) In most glaciers the swiftest flow is found near the glacial ri^^er. 

 This must in part be due to the fact that the ice is there generally the 



