218 GLACIAL GEAVELS OF MAINE. 



there to Rumford is from oae-fourtli to cue-half of a mile wide. It is a 

 U-shaped valley bordered by high steep hills. The fall of the stream per 

 mile is very small. A plain of well-rounded glacial gravel is found in the 

 valley all the way from South Andover to Rumford Point. For several 

 miles it lies as a level osar-plain on the east side of the valley, but for 2 

 miles north of Rumford Point it is on the west side and takes the form of a 

 plexus of reticulated ridges inclosing kettleholes and a lakelet. The fact 

 that this gravel plain does not extend across the whole valley is proof that 

 the gravel is not valley drift but is of glacial origin. Along with the 

 gravel are many cobbles and well-rounded bowlderets, and the slope of 

 the Ellis River is here so gentle that it is impossible to accept such coai'se, 

 well-rounded matter as ordinary stream wash. The portion of the valley 

 not occupied by the gravel plain is covered to a considerable depth with 

 silt and clay. The base of the gravel plain appears to underlie the clay, 

 but in places along the margin of the plain the gravel can be seen to over- 

 lie the clay. The great breadth of the level portion of the Ellis River 

 Valley as compared with the drainage basin makes it certain that the fluvi- 

 atile drift would be fine and the river currents comparatively gentle, even 

 in time of flood. This makes it more probable that the deposition of the 

 gravel overlying the clay took place in a broadened osar channel than that 

 it was the work of the Ellis River after the melting of the ice. 



For about 3 miles ivom Rumford Point to the mouth of the Concord 

 River there are occasional low ridges and hummocks of gravel on the Avest 

 side of the Androscoggin River. They rise out of a low terrace of erosion 

 and externally appear like nneroded portions of the plain of valley drift 

 which originally must here have bordered the Androscoggin. But exam- 

 ination shows that they are composed of gravel, cobbles, and even bowl- 

 derets — ^much coarser matter than is contained in the alluvium of this part 

 of the Androscoggin Valley. They are therefore glacial gravel. It is thus 

 proved that the course of the glacial river crossed the Androscoggin River 

 at Rumford Point. If the osar-plain was originally deposited continuously, 

 it has since been eroded by the river. This must have happened since the 

 Valley Drift period, for the upper alluvial terraces of the valley for many 

 miles below this point do not contain gravel similar to that of the osar- 

 plain. For a short distance north of the mouth of Concord River a two- 

 sided ridge of well-rounded gravel and cobbles lies parallel with the 



