204 



GLACIAL GEAVBLS OF MAINE. 



assign tliem to a single glacial river, although the sa,me river can be 

 conceived as running two independent careers at different times. 



The vicinity of Lewiston is a favorable locality for studying the dif- 

 ferences between the glacial gravels and the valley drift. Only two theories 

 can be admitted as accounting for the ridges and mounds of gravel and 

 cobbles of the Lewiston series — they are either glacial gravel or they are 

 uneroded fragments of an ancient sheet of valley alkndum. 



1. From Bethel to the sea the alluvium of the upper terraces of the 

 Androscoggin Valley is in general either sand or clay. For a short distance 

 below where the river has cut through ridges of till, there are limited areas 

 of gravel, also at the parts crossed by glacial gravel systems or near the 

 mouths of the swifter tributaries. Low terraces of sand and gravel are 

 found along the banks of the river, reaching 5 or 10 feet above it, but 



nowhere below Bethel does the low flood- 

 - ^ '.i^f^'^°" •^.'°° jli-'-r^°o- vg^^rf% plain terrace contain any such rounded 



cobbles or bowlderets as are found in the 

 ridges of the Lewiston sei'ies, except where 

 crossed by osars and near the mouth of 

 Swift River. The stones of the flood-plain 

 terrace and those in the bed of the river 

 are not nearly so much rounded, arid many 

 of them have till shapes, with but httle 

 modification by water action 



2. The two-sided i-idges and mounds of gravel, cobbles, and bowl- 

 derets of the Lewiston .series cover but a small part of the valley — here 

 and there a dot, so to speak. If they are uneroded portions of a sheet of 

 similar matter Avhich formerly filled the A^alley to a height of about 100 

 feet, then there has been a vast erosion of coarse matter from the valley, 

 and this ought to appear as plains of such material in Brunswick and Bow- 

 doinham and along the shores of Merrymeeting Bay, where the Andros- 

 coggin unites with the Kennebec. But those regions show only fine 

 sediments — sand and clay. 



Two-sided ridges and domes rising 50 to 100 feet above the level 

 ground on all sides of them can not be any form of beach terrace or sea 

 wall. Their forins and situations make this impossible. In short, these 

 gravels can not be any form of marine or ordinary fluviatile drift. 





Fig. 



-Stratificatii 



of lenticular gravel. 



