460 GLACIAL GRAVELS OF MAINE. 



RETICULATED EIDGES WITHIN ICE CHANNELS. 



Near Dover South Mills the Moosehead Lake osar divides into two 

 branches, each not more than 100 to 250 feet wide at the base. They 

 continue a few rods apart for about a half mile southeastward, when they 

 unite to form a single ridge which presently expands into a broad, almost 

 delta-like plain of sand and gravel near The Notch. Both ridges have 

 rather steep slopes on each side, and they inclose a long, narrow hollow or 

 ravine. 



I have before described the three small gravel plains in the northeastern 

 part of Monmouth. They are about one-fourth of a mile, or somewhat 

 less, in diameter. Each is crossed by a central ravine flanked by terraces 

 about one-eighth of a mile wide. My interpretation is that here a rapid 

 stream flowed into a small glacial lake, dropping its sediment on each side 

 and lea^dng the ravine where its bed was. Can we apply this interpreta- 

 tion to such a case as that at Dover South Mills ! 



If a body of still water existed at each outer flank of the two ridges, 

 there ought to be a broad flanking terrace on each outer side; if swift 

 streams, there ought to be two parallel ridges outside of the two existing 

 ridges. The outer flanks of each ridge must, therefore, have been flanked 

 by ice, and we are compelled to suppose that a single swift river flowed 

 through the central hollow or ravine, dropping a ridge on each side, and 

 its size and velocity were such for half a mile on a gentle up slope that it 

 was able to keep its channel clear of sediment Avhile building up ridges on 

 each side from 10 to 30 feet in height. Now in Monmouth the central 

 ravines, which I infer mark the beds of the streams, are not more than 20 

 feet deep in any place, and generally are rather less than 10; their length 

 is only half that of the ridge in Dover, and the beds consist of gravel; hence 

 in the process of deposition it is evident that the streams built up a plain of 

 sediment beneath them, though the finer sediment passed out obliquely into 

 the bordering lake. In Dover the ridges are in places confluent at their 

 bases, but at the deeper hollows the ravine goes down to the till, or nearly. 

 I leave the interpretation an open question until other cases are examined. 



At the Whalesback, Aurora, we have two and sometimes three ridges 

 extending for 3 miles or more, and nearl}^ jjarallel. In places the hollows 

 between the ridges are filled with gravel nearly to the top of the ridges ; in 



