SYSTEMS OF GLACIAL GRAVELS. 135 



fourth to oue-lialf mile wide is found on the west side of Pleasant River a 

 short distance east of Milo Village. A line of clay covers the Piscataquis 

 Valley from Howland to Milo, and then silty clay extends up the Piscataquis 

 to Dover and up the Pleasant River to Brownville. The gravel of the 

 plain east of JMilo Village is so much coarser than the drift of the Pleasant 

 River Valley north of the plain for several miles, and the slopes of the 

 valley are so gentle, that it is quite certain this plain is glacial gravel. The 

 plain shows several of the characteristics of the delta. The Pleasant River 

 glacial gravels do not seem to have connections south, a fact which strongly 

 supports the conclusion that they were terminated by delta-plains at the 

 ice front during the final melting and recession of the great glacier. 



LILLY BAY-WILLIMANTIC OSAR. 



A medium-sized ridge leaves Moosehead Lake at Lilly Bay. The 

 gravel is here not much rounded. The ridge is described as following a 

 rather crooked line of low passes southward, and then down the valley of 

 Wilson Stream, expanding into broad plains in Willimantic, west of Sebec 

 Lake. No glacial gravel extends along Sebec Lake and Stream, and I 

 can not trace any extension of this system south into Guilford or Dover. 

 This makes- it highly probable that the broad sedimentary plain of Wilson 

 Stream above Sebec Lake is really a frontal plain composed of matter 

 poured out by glacial streams into the valley in front of the ice, at a time 

 when the ice had retreated to this place. There is very little alluvium of 

 any kind along Sebec Stream, the outlet of Sebec Lake, until we come east 

 to within 2 miles of jMilo A^illage, when the valley widens and is covered 

 with silty clay continuous with that of the Piscataquis and Pleasant River 

 valleys. This clay is just such a deposit as would be formed in the valley 

 by the Gletschermilch of glaciers still existing- 20 miles or more to the 

 north. 



We now pass beyond the region included between tlie two princijjal 

 branches of the long- Moosehead Lake-Penobscot Valley system. 



ETNA-MONROE SYSTEM. 



We now reach a part of the State where those parts of the gravel sys- 

 tems which contain gaps as a constant and conspicuous feature are as long 

 as or longer than those parts where the ridge is continuous. 



