30 GEOLOGY OF OHIO. 
nels are continuous, and, though not necessarily of uniform depth, show 
no such succession of deep pools and rocky barriers as are imagined by- 
Professor Andrews to exist. Indeed, it is inconceivable that any such 
alteration of transverse rocky barriers and pits, one hundred feet or more 
in depth, could be formed in a country where the rocks are so nearly 
horizontal as they are in south-eastern Ohio. | 
It is true that every water-fall formed by a harder stratum overlying a 
softer one scoops out the latter to a considerable depth, but the fall con- 
stantly recedes by the wearing away of the shelf over which the river 
pours, and the excavation below, as ahove, is nearly horizontal. If the 
channel of any stream in which there is a succession of falls formed by 
horizontal hard layers be carefully examined, the rock bottom will be 
found to form a series of steps, and not of ridges and pits. The water 
may be of very unequal depth, because loose material accumulates un- 
equally in the channel, but the fall recedes horizontally, and cuts, as it | 
goes, toa nearly uniform depth. It will be remembered that the excava- 
tions of the rock bottom of the Muskingum, brought to light in building 
the dams, were longitudinal and not transverse, and that some of the 
dams were built over channels of unknown depth, cut up and down the 
river through layers of hard rock. There is scarce the shadow of a doubt 
that if a series of transverse sections were made of the valley of the 
Muskingum, that there, as elsewhere, the old deep channels would be 
found to be continuous. 
GLACIAL EROSION. 
In Chapter XXX of this Report the evidences of glacial action in 
Ohio, and the country north and east of it, are very fully described, and 
it was there shown: First—That the planing and grooving of the sur- 
face rocks, so frequentiy seen north of the Ohio river, were produced by 
ice, since they are precise copies of the inscriptions made by this agent 
in different parts of the world, and such as are not made by any other 
cause. Second—That these marks were produced by glacier-ice, and not 
icebergs, was also proved by their identity with the peculiar inscriptions 
made by glaciers, and by cases where the glaciation is visible on 
vertical and overhanging surfaces, where it could only have been pro- 
-duced by some moving mass which moulded itself to the form of the 
object against which it pressed. To those who have seen the roches 
moutonnées—the planed, grooved, and striated surfaces produced by recent 
glaciers, and who have examined the markings on the surface rocks of 
the region about the great lakes, no argument is necessary to prove 
that both sets of phenomena were produced by the same cause, and yet 
