224 GLACIAL GRAVELS OF MAINE. 



ridge lias escaped erosion, and if fresh exposures can be found they will 

 probably show a mass of coarse matter at the bottom of the ridge, perhaps 

 an osar with arched cross section. We have already seen that these erosion 

 ridges are common in the osar-plains, as in the valley of Martins Stream 

 between Livermore and North Turner, and the whalebacks in Rumford, 

 Milton, Bethel, and Woodstock. In the last-named cases it is quite easy to 

 determine that they are ridges of erosion carved out from the original osar- 

 plains. Here we find that the Little Androscoggin is larger than the 

 streams flowing in the valleys just named. Did it deposit the alluvial plain 

 below Snows Falls as valley drift! Its drainage basin above South Paris 

 covers only a few townsliips, and even in the Valley Drift period its flow 

 was small as compared with that of the Androscoggin and Kennebec rivers, 

 yet it is bordered by an alluvial plain nearly as large as theirs at the same 

 distance from the shore of the sea of that period. There are in the State 

 great numbers of streams having as large drainage basins as the Little 

 Androscog'gin above Soutli Paris, yet having very much smaller alluvial 

 plains. This gives an antecedent probability that the alluvium of this val- 

 ley is largely glacial. 



The gravel along the center of the valley below Snows Falls is well 

 rounded, like that of the osar-plain northward. But- in many places I 

 noticed that near the margin of the alluvial plain the gravel was but little 

 worn, in some cases the till shapes being hardly modified at all, and the 

 drift was almost morainal. This marginal drift resembles the ordinary 

 valley drift of streams having no greater fall than the Little Androscoggin 

 in Paris, and is just such work as could be expected of the river after the 

 ice had melted, or at the extreme margin of the broad channel of an osar- 

 plain. 



We have, then, . field evidence of distinctively glacial gravel to within 

 4 miles of South Paris, and we know that a great glacial river flowed south- 

 ward in the valley. General analogy, as well as the local facts, indicates 

 that the central part of the alluvial plain of the Little Androscoggin north 

 of South Paris is an osar-plain, deposited in a broad channel between ice 

 walls. Later, as the ice melted, the water extended across the whole 

 valley. Alluvium was then deposited mainlj^ at the sides of the osar-plain, 

 and it was subjected to much less attrition than were the stones of the older 

 glacial gravel. It would naturally happen that after the ice had all melted 



