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 thestream. 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 
