422 GLACIAL GRAVELS OF MAINE. 



down the terminal ice slope. If the glacier continues to retreat, it seems 

 probable that a ridge or series of ridges such as are now forming and aban- 

 doned channels of these rivers will be prolonged northward as far as the 

 englacial channels reach. This furnishes an observational basis for the con- 

 clusion that during the retreat of the ice-sheet, wherever the ice was very 

 stagnant and the subglacial streams found their tunnels choked near their out- 

 lets, they freely rose into englacial or superglacial channels. Since in doing 

 so they would naturally wander more or less from the course of the original 

 tunnel, a plexus of ridges would more often be formed than a single ridge. 



Now some of the shorter osars of Maine belong to regions lying north 

 of transverse hills, where, after the hills in front were bare, the ice must 

 have been somewhat stagnaiat and the conditions would be favorable to the 

 formation of marginal ice canyons of this class. But the longer osars go 

 up and over hills, and some of them occupy the longer north-and-south 

 vallej^s, where the ice flow would be rapid and subglacial streams would be 

 easily formed anywhere near the ice front. 



One other class of superficial channels in which it is supposable that 

 osars were deposited is due to waters of superficial melting cutting canyons 

 in the ice down to the ground. At one time I considered it a probable 

 h^^pothesis that in a country like the interior of Maine, where the ice over- 

 flowed so many transverse hills, the subglacial streams would not readily 

 develop, and that here were the proper conditions for surface streams to 

 continue to flow until near the final disappearance of the ice. The Mala- 

 spina glacier makes it difficult to maintain that contention. It is not admis- 

 sible that there were in Maine any more favorable conditions for surface 

 streams than that glacier affords, except that the summer melting may have 

 been more rapid in the more southern latitude and that there was less water 

 warmed on bare land to go down beneath the ice to enlarge the subglacial 

 tunnels. If on so stagnant a glacier with so narrow crevasses the surface 

 waters are able to find their way into the subglacial tunnels, it must be 

 admitted to be improbable that large surface streams could exist anywhere 

 near enough to the margin of the glacier to have reached the englacial 

 matter of the ice- sheet, unless under extraordinary conditions that could 

 have prevailed only for a limited time and over limited areas. The con- 

 clusion follows that the great length of the osars of Maine favors the 

 hypothesis that they were mainly formed in subglacial tunnels. 



