80 



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 above, 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 loater 

 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, to a 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 doion 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 EEOSION. 



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 frequently 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 

 •moutonn'ees — 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 



