HARTLAND-MONTVILLE SYSTEM. 157 



Hogback Mountain Pass, flow simultaneously? I was unable to find any 

 conclusive facts in the field. Two reasons can be given why it is probable 

 that the Liberty branch was the earlier. 



1. The delta-plains of this system seem to date from a time when the 

 ice had not receded so far north as at the time' the North Searsmont Plain 

 was being deposited. 2. The glacial stream which formed the last-named 

 plain flowed not only down a valley of natural drainage, but parallel with 

 the direction of glacial flow. The gravel, too, is scanty for some distance 

 on the steep down slopes, so that the glacial chaiuiels did not there become 

 clogged with sediment. I see no reason why this stream should cease to 

 flow, or why, after it once had been established, it should not carry away 

 all the water that poured southward through the pass. On the other hand, 

 the southwestern channel was over higher ground, and for a time was trans- 

 verse to the lines of flow of the ice. At any time the south channel should 

 be opened this stream would cease to flow, except possibly when the water 

 was very high. The history of the gravel plain at the south end of the 

 pass is probably about as follows: Originally the glacial river flowed by 

 the southwestern channel and solid ice blocked the valley of the east 

 branch of Georges River. Then a lake was formed within the ice at the 

 south end of the pass, in which was deposited the coarse matter of the 

 plain, or a part of it. The lake gradually enlarged, so as finally to extend 

 for one-fourth mile or more eastward into the valley of the east branch of 

 Georges River, which, as already stated, extends eastward from the south 

 end of the Hogback Mountain Pass. In this enlarged lake was deposited 

 the thick sheet of sedimentary clay aiid silt which covers this valley to the 

 east of the pass. Finally the barrier of ice in the valley was in some way 

 penetrated toward the south and a new channel was established down the 

 valley to Center Montville and to the sea near North Searsmont. This 

 channel would naturally come to be lower than the other, so that it would 

 carry off all the water of the glacial lake, except in times of great floods, 

 when the southwestern channel might still, for a time, serve as an overflow 

 channel. In process of time the south channel would become enlarged so 

 as to take off all the water by the lowest route. All the field phenomena 

 could be produced by two streams flowing simultaneously. But. much the 

 larger stream flowed southwest, and it deposited far more gravel than the 

 other. These facts favor the conclusion that it flowed much longer than 



