478 GLACIAL GRAVELS OF MAINE. 



in the hills of Oxford and northern York counties three great north-and- 

 south osar series are connected every few miles by transverse lines of 

 gravels, several of which follow the east-and-west valleys. But in general 

 we must suppose that the latest channels of deflection were in use for too 

 short a time to become enlarged sufficiently to permit within them the 

 deposition of gravels. 



For various reasons, then, the Avaters of the longer osar rivers often 

 did not form frontal or overwash gravels in front of the ice during the 

 retreat. If they had continued to flow up to the last, the gravels previously 

 deposited Avithin channels in the ice ought to have been covered or flanked 

 by matter poured out in front of the ice during the retreat. That this did 

 not happen is best explained by supposing the streams to have been diverted 

 to new channels at some time not long previous to the final melting of the 

 ice at those places. Below the level of the sea it would facilitate inter- 

 pretation if we could assume that some of the rivers ceased to flow in 

 consequence of the pressure of the rising sea, also if we could assume that 

 toward the last the melting of the ice in the far interior valleys of the State 

 was more rapid below sea level than above it. This would be equivalent 

 to the formation of bays of the sea penetrating into the ice beyond the 

 general frontal line, a condition that would facilitate interpretation at 

 Oxford and elsewhere. Such an outline would not be inconsistent with 

 the lines of frontal retreat as set forth elsewhere, but thus far I do not 

 find direct proof of it, unless through the evidence furnished in some cases 

 by the osar border cla}'. 



2. The absence of osars in north-and- south valleys proves that the 

 channels of the glacial streams had not become sufficiently enlarged to per- 

 mit deposition within them. The streams must have transported all their 

 sediments to the ice front and pom-ed them out as frontal overwash or valley 

 drift. Where these streams were united into one main river we would find 

 the coarsest matter arranged along the course of the stream, and the sedi- 

 ments would grow finer on each side. The coarser mass would not have a 

 definite border or arched cross section. Where there were several glacial 

 streams there would be a corresponding number of coarser belts. Under 

 some conditions these might form reticulations and inclose lake basins and 

 kettleholes, like those in the valley of the Andi-oscoggin River in Shelburne, 

 New Hampshire. These would often be filled later by other drift, but 



