TOPSFIELD OLD STEBAM SYSTEM. 91 



into Big Lake, there is a thin sheet of gravel on a gentle slope rising but a 

 few feet above the lake. This gravel lies a full half mile south of the 

 osar. The stones are distinctly water-polished, though differing little from 

 tillstones in shape. This deposit is an old beach, either marine or lacustral. 



The osar leaves the Musquash Valley about a mile north of Big Lake 

 and takes a nearly straight course southwestward. It is easily traceable for 

 several miles along the northwestern shore of Big Lake, often forming the 

 beach. The gravel reappears on the southwestern shore of the lake, 

 between Little River and Little Musqiiash Stream, and continues its south- 

 westward coin-se for several miles along the valley of Little River. It then 

 crosses a low divide and extends for many miles southward along Old 

 Stream, expanding into extensive plains of reticulated ridges near the Old 

 Stream Lakes. The sand and gravel plains extend to the junction of this 

 stream with the Machias River, and toward the south are quite level on the 

 top and present the appearance of a marine delta-plain. 



A series of discontinuous and rather flat-topped plains or broad ridges 

 extends from neai; Masons Bay, Jonesboro, northward into Centerville. 

 They appear to be marine delta-plains, deposited not in the open sea but 

 in bays receding backward into the ice. They are probably a continuation 

 of the Topsfield-Old Stream system. 



The extensive marsh region penetrated by this gravel system is under- 

 lain in considerable part by sedimentary clay. Big Lake is 189 feet above 

 high tide. Hence, when the sea stood at 225 feet, a sheet of salt water 

 must have extended up the valley of Schoodic (also called Kennebasis) 

 River to a point a short distance west of Big Lake, and at an elevation of 

 about 36 feet above the present level of the lake. The region around the 

 lake, especially toward the south and southwest, is so low that a body of 

 water of that elevation would be very much larger than the present lake. 

 The divide between Little River and Old Stream is low, but probably not 

 low enough for an arm of the sea to have extended from Big Lake down 

 the Old Stream and Machias valleys. The region overgrown with pine 

 near Clifford Lake, which I formerly supposed was covered with glacial 

 gravel, now appears to owe its sand and gravel to the action of the waves ; 

 they are probably beaches of that period. There is an enlargement of the 

 osar near the northwestern angle of Big Lake. Part of this appears to be 

 a small delta. If so, the history of the Topsfield-Old Stream glacial river 



