SIZES OF VALLEY-DRIFT KIV^EES. > 489 



Below Moscow and Bingham the sedimentary phiin of the Kennebec 

 is from 1 to 6 or 7 miles wide. The overflow stream from Bethel south- 

 ward into Albany was a fourth of a mile wide or more. This was an over- 

 flow of the Androscoggin River. Even if we admit the alluvium of the 

 broader A^alleys to be fluviatile marine deltas, still we need streams capable 

 of acting over great breadth and with velocity suflicient to transport gravel 

 and cobbles. The breadth and character of the deposits demand large 

 rivers, but I am not prepared to submit a quantitative comparison between 

 them and those of to-day. It is probable that there was a greater rainfall 

 then than now, if we correlate valley-drift time Avith a part of the career of 

 lakes Bonneville and Lahontan. But we know neither the cause of the 

 glacial epoch nor the cause of its termination. At present I leave open 

 the question of the sizes of valley-drift rivers as compared with those of the 

 present time. 



