246 IRVING B. CROSBY 



with the general trend of the topography. This region has not 

 been studied in detail, but it appears probable that in preglacial 

 times there was a river following a course similar to that of the 

 present Androscoggin, between Livermore Falls and Lisbon Falls, 

 and emptying into Casco Bay. This preglacial stream with the 

 Little Androscoggin was the principal river between the Sebago 

 and the Kennebec. 



The Androscoggin River east of the mountains now occupies 

 parts of two preglacial drainage systems. The main valleys of 

 these two systems were clogged with drift in many places and the 

 resulting drainage follows a circuitous route and empties into the 

 Kennebec with a retrograde course. 



CONCLUSIONS 



This study has shown that the present course of the Andros- 

 coggin River is largely postglacial in origin. 



It appears that in preglacial times there was a low divide at 

 Mount Winthrop on the northeastward continuation of the main 

 ranges of the White Mountains. All the drainage northwest of 

 this divide went to the Connecticut River, passing through the 

 valley now occupied by the Upper Ammonoosuc. This drainage 

 system, including the Androscoggin above Dummer and the stream 

 from Mount Winthrop Divide, is here called the "Mahoosuc" 

 system. 



Eastward from this old divide a stream flowed to Bethel where 

 it was joined by a branch from the valley of Sunday River; and 

 the stream resulting from their union, here called the "Sebago 

 River," flowed southward through the valley now occupied by 

 Crooked River, through the basin of Sebago Lake and into the 

 ocean near Old Orchard. 



East of the Sebago system was a north-south stream which 

 with its tributaries, including the Little Androscoggin, drained 

 nearly all the region between the Sebago and Kennebec rivers. 



East of Bethel the drainage lines were greatly disarranged 

 by heavy deposits of glacial drift. A single stream may occupy 

 portions of several preglacial valleys and have other portions of 

 its course of postglacial origin. 



