458 GLACIAL GRAVELS OF MAINE. 



sunliglit. This makes it all the more difficult to account for the wanderings 

 of a single superglacial river when it has cut a channel to the bottom of 

 the ice, or nearly so, and that, too, very near the ice front. The narrow 

 marine delta could, perhaps, sometimes be accounted for on the superglacial 

 hypothesis, for the melting would probfibly be most rapid near the mouth 

 of the main river, thus prolonging a narrowly deltoid bay or channel back 

 into the ice and open to the sea in front. Ice gorges might possibly bar a 

 superficial channel so as to cause an overflow into a new channel, but it is 

 difficult to suppose that a dam of loose blocks would last long enough to 

 enable a new channel to be cut to the bottom of the ice. If we assume 

 that the channel became blocked by the coarsest sediment where it entered 

 the sea, what are we to do about the sediment at the distal end of the delta, 

 which evidently went over this supposed bar on its way south? 



On the whole, the difficulties of the superglacial hypothesis are greatly 

 increased by the breadth of the northern ends of some of the marine deltas 

 and the certainty that they were enlarged, not by radiate transportation in 

 the sea beyond the ice front, but by a single glacial river issuing from the 

 ice by several mouths, the more distant being a half mile or more from each 

 other. How far the flow of these different streams was simultaneous, and 

 how far successive, is left an open question. 



Usually marine deltas are a part of the discontinuous portions of osars; 

 hence often there are intervals to the north of them without gravels. Here 

 we have the same problem of noncontinuity as in the case of the other dis- 

 continuous deposits. Some of the deltas, perhaps, began as massive bars or 

 mesas in gradually enlarging glacial lakes into which the sea subsequently 

 advanced as the ice front retreated, after which time the deltas proper were 

 deposited. 



5. Were all the reticulated ridges at the landward ends of the glacial 

 marine deltas deposited in the sea? 



As above noted, there are sometimes gaps in the systems north of the 

 deltas. In these cases I conceive that the rapidity of the streams was here 

 sufficient to keep their channels free from sediment. These conditions 

 probably prevailed all the way to the ice front, and in such cases all the 

 reticulated ridges were formed in the sea. 



But where long ridges extend northward from the proximal ends of the 

 deltas, especially complexes continuing up to considerable heights above 



