FORMER COURSES OF THE ANDROSCOGGIN RIVER 245 



gentle gradient broken by falls, while the Sebago River has a con- 

 stant grade without falls, indicating that the present course of the 

 Androscoggin is partly at least of recent origin and that the course 

 of the Sebago River was for a long time occupied by a large stream. 



There is no obstacle today except glacial drift to prevent the 

 Androscoggin from following its old course and a dam 40 feet high 

 at Bethel would enable it to do so. 



Sebago Lake is drained by the Presumpscot River, a short 

 stream with seven falls and an indirect course. It is at once seen 

 to be a postglacial stream without a rock valley, and it can be dis- 

 missed as a possible course for the Sebago River. 



On the south side of Sebago Lake is Sebago Lake Station, where 

 the Main Central Railroad crosses a very low divide. A rise of 

 20 feet in the lake would cause it to overflow here. The topography 

 is typical of a terminal moraine; kames and kettles are numerous, 

 and there are several kettle ponds. 



This morainal dam marks the preglacial outlet of the Sebago 

 Basin and the rock valley which the moraine now fills was undoubt- 

 edly the route of Sebago River. 



Between Sebago Lake and the ocean the old valley is lost under 

 a heavy mantle of till and extensive marine deposits. There are 

 well-developed marine terraces at several levels near the coast. 



The old valley probably reached the present shore in the vicinity 

 of Old Orchard, where there is a broad indentation of the coast 

 with no rock outcrops over a considerable area. Offshore soundings 

 tend to confirm this view. 



The valley of Sebago River from Bethel to the ocean has been 

 located and described as fully as conditions permit. It presented, 

 before being clogged with glacial drift, a natural course for a large 

 river and is more probable as the preglacial course of the Andros- 

 coggin than the present route. 



The Sebago River, which made this valley, had little in 

 common with the present Androscoggin. One branch came from 

 the Mount Winthrop Divide to Bethel, where it joined a branch 

 from the valley of Sunday River. 



South from Livermore Falls through Lewiston the present 

 Androscoggin has a fairly direct north-south course in agreement 



