SURFACE GEOLOGY. 44Aq 
This I suppose to be the law of erosion in rocks of unequal hardness, and 
has innumerable illustrations. | 
Any elevation of the continent would not tend to change this law, 
although such elevation is required for the explanation of the erosion of 
channels and of bays now below the level of the sea. But inland, and in 
regions so high that the streams could not be affected by any back or 
dead-water, the drainage has always been the same as now. The erosion 
of the pools in the softer rocks would, after a time, reach its maximum, 
and the pools would gradually fill up with sand and mud, and then the 
chief erosion would be on the hard strata of the intervening ledges, re- 
ducing them slowly to the common level of the bed of the stream, to be 
covered in time with alluvial materials. In our larger streams only a 
few of the old rock barriers are now to be seen, but there are doubtless 
large numbers which are covered with only a few feet of sand or mud. 
The work of erosion in southern Ohio has been going on ever since the 
Carboniferous era, and it has been, consequently, very great. Standing 
on the summit of one of our high hills, we may look for miles across in- 
tervening valleys to some distant knob, and realize that by the slow pro- 
cess of surface drainage the rock strata which once connected the two 
points have been removed. The tops of anticlinals, such as the Newell’s 
Run uplift in Washington county, have also been removed by the same 
slow agencies. A few miles south of the Ohio River, in West Virginia, 
the continuation of the Newell’s Run anticlinal ridge was once 4 narrow 
mountain a thousand feet high above the present streams. It has been 
eroded away, leaving hills no higher than the others in the neighborhood, 
and these wre intersected in all directions by valleys. 
In these ancient valleys of southern Ohio, and doubtless over the hills 
as well, there was a growth of vegetation, and trunks and branches of 
trees indicate a forest growth. These remains are found both in the 
alluvial materials at very considerable depths, and also in the blue clays 
of the Drift. It is, however, improbable that these valleys were ever 
occupied by moving glaciers, for such glaciers would entirely sweep 
away all the local vegetation. The short, sharp curves of many of these 
valleys would apparently entirely prevent any glacial motion in such 
deep and crooked river beds. In the subsidence by which the land was 
lowered so that the waters could bring in and deposit as sediment the 
blue clays, the overthrow and burial of the old forest trees of the valleys 
took place. This was the first work of the Drift period, as recorded in 
south-eastern Ohio. These waters were connected with a great northern 
subsidence, and in the waters of this sea was floating northern ice, from 
which bowlders were dropped into the same mud, which buried the old 
