A BRIEF HISTORY OF THE OHIO RIVER. 



741 



rents, leaping from ledge to ledge, or dashing round and over 

 masses of rock in their wild mountain homes. Lower down the 

 current slackens, some of the impetuosity is lost, but it still glides 

 swiftly over its rocky bed. Still lower down the current becomes 

 slower, the stream broadens out, and the bed loses its rocky and 



Ideal view of an Old Unglaciated Coun- 

 try, SHOWING THE FORM ASSUMED BY THE 



Eminences when Erosion has proceeded 

 to a great extent. (United States Geo- 

 logical Survey.) (Chamberlin.) 



A Country, in contrast with the adjacent 

 Figure, in which the Drainage has been 

 disturbed by Glacial Deposits, and the 

 Streams are beginning to wear new Chan- 

 nels. (Chamberlin.) 



rugged character ; while as the mouth is approached the current 

 becomes sluggish, broad bottoms appear, a greater width to the 

 stream is apparent, and all signs point to the end of its career- 

 As with the course of a river, so with its life. In early days, be- 

 fore the channel is well defined, it is a foaming torrent. Later on 

 it smooths its bed and becomes more stable in position. As years 

 and centuries pass away, the rougher places are leveled, and the 

 stream then flows placidly in its course over its well-worn, often 

 deeply excavated channel. The Ohio has reached this last stage 

 in its history, for at only a single place in all its course from 

 Pittsburg to its mouth does its channel show signs of a rocky 

 character. The reason for this single exception will soon become 

 clear. 



An examination of the geological structure of the country 

 through which the Ohio flows shows none but the extreme end of 

 the valley to be of later age than the Carboniferous. Portions are, 

 indeed, far older ; but the area covered by these, though perhaps 

 extensive enough to allow the development of some system of 

 drainage, was never large enough to develop a stream of any 



VOL. XXXVIII. 61 



