136 GEOLOGY OF OHIO. 



localities. In some places, as near Campbellport, the Drift deposits are 

 largely made up of angular or little-worn fragments of sandstone, torn 

 from their beds in the immediate vicinity ; while in places remote from 

 such outcrops of the harder rocks, the stones contained in the clay are 

 small, much worn, and many of them are composed of granite, etc., 

 brought from the region north of the lakes. 



On the highlands the gravel beds referred to above rest sometimes on 

 the bowlder clay, but perhaps oftener on the underlying rock, showing 

 that the causes which produced the accumulation of gravel generally 

 removed all the clay. Where the gravel beds overlap the bowlder clay, 

 the materials which compose them seem to have been washed back from 

 the higher grounds. It will be noticed that the pebbles in the gravel 

 beds are well rounded and often irregulary stratified, while those found 

 in the bowlder clay are sub-angular, scratched, and worn, but rarely 

 rounded. It is evident, therefore, that the gravels have been subjected 

 to a triturating action quite different from that exerted by glaciers on 

 the materials which they move. The facts show, further, that water, either 

 in shore waves or in river currents, has been the agent by which the 

 pebbles of the gravel have been rounded ; and as it is difficult to conceive 

 of any currents which could leave beds and hills of gravel such as are 

 found along the divide between the waters of the Lake and the Ohio, I 

 have been led to consider these deposits as the effect of shore-waves, 

 when the Lake basin was filled to this height, on the bowlder clay and 

 other Drift material which once covered the underlying rocks. It is pos- 

 sible, too, that the drainage from the glacier, when it filled the lake 

 basin and was melting along its southern edge, contributed to the wash- 

 ing of the clay and the rounding of the pebbles. In this view the gravel 

 hills and sheets which cover so much of the great divide which crosses 

 the State may be compared to the terminal moraines of existing glaciers, 

 but in no moraine of which I have any knowledge are the pebbles and 

 bowlders nearly so well rounded as in the deposits under consideration ; 

 and I am sure all who will carefully examine these will agree with me 

 that free arid swift, moving water, in large quantity, has been the chief 

 agent in producing the phenomena exhibited. Along certain lines lead- 

 ing from the summit of the watershed to the Ohio, both east and west of 

 Portage county, there are belts of gravel and bowlders, which mark, as I 

 conceive, broad and long-existing drainage channels, by which the sur- 

 plus water of the lake basin flowed through certain waste-weirs cut in 

 the watershed, escaped southward, but the gravel hills of Portage county 

 can hadly be referred to such a cause. 



