20 GEOLOGY OF OHIO. 



bergs, which in the last great submergence seem to have carried their 

 freight, in some instances, beyond the points reached by the glaciers, and 

 especially by the action of local currents of water which flowed down 

 through certain great lines of drainage, the Drift materials have been 

 borne far beyond the line I have indicated as bounding the erosive action 

 of the ice-sheet. In the valleys of the Beaver, the Muskingum, the 

 Hocking, Scioto, and Miami, we find vast accumulations of Drift, which 

 are, however, confined, in the lower part of these valleys, to the immedi- 

 ate vicinity of the stream. Here they form terraces which rise sometimes 

 a hundred feet above the present stream beds, and they undoubtedly filled 

 the old deeply excavated channels through which these streams once 

 flowed at a much lower level than now. In the valley of the Ohio itself, 

 also, we find similar accumulations of Drift, composing the terraces so 

 noticeable to one who passes up or down the river, and also filling the 

 old rock channel to the depth of from 100 to 200 feet. The terrace on 

 which the city of Cincinnati stands, and which has an altitude of 100 to 

 120 feet above low-water mark, will serve as a good example of the gravel 

 terraces to which I have referred. In all the valleys enumerated above, 

 the Drift material has evidently been washed down from the highlands 

 of the interior of the State, where the Drift deposits are continuous and 

 of considerable thickness. Hence it is more properly termed Modified 

 Drift, or Valley Drift. By the action of the streams which transported 

 it, the valley Drift was assorted and rearranged, and exhibits no record of 

 the series of important changes of which the history is written in the 

 sequence of Drift deposits where these remain undisturbed. Very natu- 

 rally, the swift-flowing streams which have carried the Drift so far 

 from their original place of deposition have washed out all the finest 

 material, and have deposited this far beyond the limits of our State. 

 We therefore find but little clay in the valley. Drift. It is composed 

 mainly of gravel and bowlders, with more or less sand, and the materials 

 are all rounded, as they would necessarily be, from the attrition to which 

 they have been subjected. They also exhibit an interesting gradation 

 of fineness as we follow these streams down toward their mouths. In the 

 valley of the Ohio, at Louisville, the Drift material found in and along 

 the river bed is all fine, and bowlders of sufficient size to form cobble- 

 stone pavement are comparatively rare. Many of these are composed 

 of granite, greenstone, quartzite, etc., which have been brought from 

 beyond the lakes, and only the hardest and toughest of these meta- 

 morphic rocks have resisted the wear to which they have been subjected 

 in their long journey. At Cincinnati the valley Drift is sensibly coarser 

 than at Louisville, though still fine, as compared with that which is found 



