256 



Chamherliji and Leverett — Studies of the 



iferous conglomerate (in places reaching as much as 75 feet), 

 while on the latter there are more easily erodible coal-measure 

 sandstones and shales. This greater hardness and resistance to 

 erosion would naturally lessen the size of the valley. It 



Map N9 3 



2 ? 6 ^t 10 



PRESENT DRAINAGE 



OF PART OF THE 



MIDDLE ALLEGHENY 



should also influence the gradient of the stream if it is an im- 

 portant factor. We turn, therefore, to the latter for light 

 upon this question. In the portion of the Allegheny where 



