212 GLACIAL GRAVELS OF MAINE. 



to the Androscoggin. I could find no proof that these sand ridges were 

 uneroded portions of a delta that once filled the valley. 



No kame material was found for a short distance near the tO]3 of the 

 pass, and then begins a series of low ridges and terraces of fine gravel con- 

 taining b,ut few large stones, and those are but little polished by water. In 

 numerous places these deposits could be seen to consist of a thin sheet of 

 gravel (2 to 5 feet thick) overlying the till. All these facts combine to 

 prove that the glacial stream that flowed south throiigh the Worthley Pond 

 Pass was very small, compared with the mighty rivers Avhicli flowed out of 

 the Androscoggin Valley at Canton and Rumford. The system follows the 

 valley of the main east branch of Twentymile River to Sumner station 

 (Sumner Flats), and then its course lies near the railroad to a point near 

 Buckfield Village. The gravel appears as low, rather level-topped ridges, 

 like a narrow osar-plain, except that they inclose some shallow kettleholes. 

 Often these plains appear like terraces on the sides of the valley, and 

 erosion of the central parts of the plain by the stream often increases this 

 resemblance. The system is somewhat interrupted by short gaps north of 

 Sumner station. South of that point the separate ridges coalesce more and 

 more, and not far north of Buckfield the system passes into a delta-plain 

 one-fourth to one-half mile wide. The sand of the delta passes by degrees 

 into the clay which covers the valley of the Twentymile River all the way 

 from its mouth to a point several miles above Buckfield. At a few points 

 not far south of Sumner excavations showed that a number of low ridges 

 had first been deposited in a separate, narrow channel, bordered by ice 

 walls. Subsequently the depressions between the ridges were filled up so 

 as to make of the whole a level-topped plain. Probably the tops of the 

 original ridges were in part washed away by the broad body of water 

 which at the last swept over the whole breadth of the gravel system, and 

 may have furnished part of the material to fill up the depressions. This is 

 a sort of structure to be anticipated for the osar-plains, bu.t in this case the 

 plain extends across the valley from side to side in such a manner as to 

 make it difficult to judge whether this plain was deposited in a broad 

 channel within ice walls or in the open valley after the ice had melted. 

 Even if the upper part of the plain be valley drift of less age than the ice 

 occupancy of that region, the underlying ridges are plainly contempo- 

 raneous with the ice occupancy. 



