398 Foshay — Preglacial Drainage of Western Pennsylvania. 



carrying off the rainfall of almost all Western Pennsylvania 

 and Eastern Ohio. 



The preglacial drainage of Northwestern Pennsylvania and 

 Western New York was long since thoroughly worked out by 

 Professor John F. Carll, who was the pioneer in this field. In 

 the course of his survey in Northwestern Pennsylvania he col- 

 lected proof* of the existence of at least two northwardly 



MAP OF THE 

 ANCIENT DRAiNAGl 



WESTERN PENNSYLVv 

 BY P. MAX FOSHAY 



•I fi #' 



flowing preglacial streams which drained the northern part of 

 the present Allegheny basin and debouched, like Spencer 

 River, into the Erigan River. The Allegheny River, as we 

 now know it, did not then exist but was formed after the 

 glacial episode, during which time the mouths of the ancient 

 northwardly flowing streams had been blocked up. This 

 blocking up of the ancient drainage forced the post-glacial 



* Report III. Second Geological Survey of Pennsylvania, pp. 330-366. John 

 P. Carll, Harrisburg. 1880. 



