416 GLACIAL GEAVELS OF MAINE. 



Most of the osar systems also expand at various distances from the 

 ■coast into marine or glacial la,custrine deltas. 



When we come within 20 to 40 miles of the coast, we find in many 

 cases large plains of reticulated kames. These are much longer than the 

 areas of reticulated ridges found farther north. They extend from 230 feet 

 up to 400 or 500 feet. At about the same distance from the coast all of 

 the osars begin to become systematically discontinuous. Southward the 

 ridges become on the average shorter and smaller and the intervals between 

 them longer, and in all but a few cases they apparently terminate near the 

 north ends of the bays of the coast and only a few feet above sea level, as 

 has been stated of the discontinuous osars. 



COMPARISON OF CONTINUOUS WITH DISCONTINUOUS OSARS. 



The osars are thus seen to be somewhat discontinuous, but not system- 

 atically so until they approach the coast. In almost all cases in the interior 

 their interruptions have a, direct connection with the slopes of the land or 

 places where there would naturally be swift currents, as where the rivers 

 crossed hills or penetrated narrow passes. But the discontinuity of the 

 coast is very different. There the sediments ai-e gathered more often on 

 the hills, while the lowlands show no gravels. Only in comparison with 

 the coastal gravels, then, are the osars continuous. 



A plausible theory of osar formation postulates that it began as a dis- 

 continuous series of separated deposits left here and there in enlargements 

 of the channel or other places favorable to sedimentation. As the channel 

 was gradually enlarged, sediments could be deposited more and more 

 frequently, until at last continuous ridges were formed. On this hypothesis 

 both the continuous and discontinuous systems began in the same way, but 

 the osars went on to a more perfect development. 



Elsewhere we stated numerous facts proving a gradual retreat of the 

 ice and forward advance of the sea and bare land. The limited amount of 

 wave erosion proves that the Champlain elevation of the sea was geolog- 

 ically brief, yet it afforded time for the completion of a large amount of 

 geological work. This fact rather favors the hypothesis that a continuous 

 ridge begins as a series of discontinuous deposits, which gradually become 

 confluent if the flow of the river is continued long enough, or at least is not 

 inconsistent with it. Yet some weak points remain in the argument. 



