OASGO-WINDHAM SYSTEM. 237 



level plain composed largely of sand and fine gravel, which near North 

 Windham is not far from 2 miles broad. South of this point the gravel 

 narrows so as to form a rather level plain about one-fourth of a mile wide, 

 which continues southward past Windham Hill to a point about one-half 

 mile south of Windham Center. Near the south end of this plain the 

 material is very coarse, consisting chiefly of cobbles with bowlderets and 

 bowlders. 



In many places in this system there are great numbers of rounded 

 bowlders 2 to 4 feet in diameter, a fact which favors the hypothesis that 

 it was deposited by subglacial streams. 



South of Windham there are several plain-like deposits of glacial 

 gravel in Grorham and Scarboro which are probably marine deltas. The 

 largest of these plains is at Grorham Village. They are in the proper posi- 

 tions to have been formed by the same glacial river that brought down 

 the gravels of the Casco- Windham system. But the country is so level 

 that we have no hills to act as barriers to confine the glacial rivers, and the 

 intervals between the plains are so long that provisionally I mark the 

 system as ending in Windham. 



The gravels of this system form, wholly or in part, the dam which 

 caused the formation of Little Sebago Lake, in Windham and Gray. The 

 original outlet of this lake flowed west into the Presumpscot River, and its 

 bed shows only glacial gravel for some distance from Little Sebago Lake. 

 An artificial channel has been dug for the purpose of taking the water of 

 the lake south into the Pleasant River, the small stream flowing from 

 Gray southwestward into the Presumpscot in Windham. This channel is 

 dug wholly in the glacial gravel. 



The North Windham Plains pass by degrees into sand, and finally 

 into marine clay toward the south and east. They are marine delta- 

 plains in part, found in the arm of the sea which extended from Windham 

 northward past Gray and joined the bay that then covered the valley of 

 Royal River. But perhaps there is a continuous plain of purely glacial 

 gravel near the axis of the area which is continuous with the Windham 

 Center Plain. 



At Raymond Village the osar-plaiu is bordered and partly covered by 

 sedimentary clay. This is at an elevation of about 20 feet above Sebago 

 Xake. There is no continuous sheet of clays at this elevation around the 



