Drainage Features of the Upper Ohio Basin. 253 



PROBABLE 



PREGLACIAL DRAINAGE 



OF THE 



UPPER OHIO REGION 



3 Mile* 



5 10 15 10 IS SO 



Map h? 2. 



decided northward descent. This singular feature may per- 

 haps be due to a recession of the Thompson col through Valley 

 excavation, as suggested by Mr. Carll (Penn. Second Geo'l. 

 Survey, Kept. Hit, p. 311), and the formation of a pseudo col 

 north of Warren at a point where excavation and consequent 



