GLACIAL PHENOMENA IN MAINE 
129 
below the general undulating level of the slate 
beds, and upon its surface there is no trace of 
rectilinear lines and grooves, but simply the 
usual irregular, winding marks arising from 
the action of running water, and following all 
the structural inequalities. The valley as a 
whole is a rather shallow depression, sinking 
a little more sharply toward the centre, and 
rising gradually east and west of the river- 
banks. The whole rock surface, with the 
exception of the river-bed, is glaciated, and it 
is impossible to overlook the fact that the 
same agent which has fashioned the bottom of 
the valley up to the adjoining hills has also 
grooved and scratched, at right angles with 
their structure, the upturned beds trending 
across it. 
The absence of angular ledges in a region 
exclusively composed of uplifted slaty rocks is 
very remarkable. Facts like these show that 
a careful survey may furnish the means of 
actually measuring the extent of denudation 
or abrasion resulting from the grinding power 
of glaciers. They may even settle the ques¬ 
tion as to the origin of lake-basins now under 
discussion among geologists. The extensive 
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