310 



THE ICE AGE IN NORTH AMERICA. 



emerging from the Tuscarawas Valley through a clearly- 

 marked buried channel leading from one valley to the other 

 at Newark. At the present time the Tuscarawas drainage 

 turns a right angle at Dresden and flowing south to Zanes- 

 ville is joined by the Licking River coming from the north- 

 west, and both flow southward through a narrow, and clearly 

 post-glacial valley to the Ohio at Marietta. 



The whole country north of Columbus is so deeply covered 

 with glacial drift that it is impossible to trace the preglacial 

 drainage except through the aid of borings which have been 

 made in search of artesian water, or of gas and oil. But these 

 have revealed so many deep canons, in some cases more than 



Fig. 95 — Cross-section from Sonora, Illinois, to A.r?yle, Iowa, showing old and new chan- 

 nels of the Mississippi River. (From Iowa Geological Survey.) 



500 feet in depth, that it is by no means impossible, or even 

 improbable that the whole drainage led off into the Wabash 

 Valley, or perhaps more directly north into the bed of Lake 

 Erie, and so around into the Wabash or Illinois. 



The preglacial drainage of the Lower Ohio is equally inter- 

 esting. As already shown, and as appears graphically in the 

 map on p. 643, the Licking River of Kentucky continued 

 north from Cincinnati through the valley of Mill Creek, hav- 

 ing been joined at Ivorydale by that portion of the preglacial 

 Ohio which came from the col below the mouth of the Scioto. 

 This united stream, after reaching Hamilton, probably turned 

 southward through the channel of the Great Miami, which is 

 much broader than that of the Ohio just below Cincinnati. 

 Below Lawrenceville, Indiana, there has been little change in 



