58 



WILLIAMS— DEEP KANSAN PONDINGS IN 



systems are called Allegheny, Tionesta, and Clarion, from the prom- 

 inent streams which compose them. Of these the last was the pre- 

 dominant stream in Western Pennsylvania. It rose on the plateau 

 of the McKean County highlands in many good-sized feeders which 

 almost met similar feeders of the Allegheny on the north side of the 

 low slopes of the plateau. In the Pittsburgh area it received the 

 waters of the Monongahela and Youghiogheny. Turning westward 

 into the valley now occupied by the Beaver, it received the stream 



Fig. 4. Map of Allegheny, Tionesta and Clarion Basins. 



now reversed to form the upper part of the Ohio, and in the state 

 of that name it occupied the valley of Grand River. It thus com- 

 pletely encircles the basin of the Tionesta-French Creek stream 

 which partly to-day forms the Allegheny. In Fig. 4 only the portion 

 from its sources to its junction with the latter is shown. 



The black indexes mark the places where water was forced over 

 watersheds by more or less deep ponding. Among these places are 

 the four trenched cols: at Big Bend (connecting the Kinzua and 

 Conewango branches of the preglacial Allegheny) ; at Thompson 



