FRANKLIN COUNTY. 645 



all the marks of mechanical violence that the igneous rocks of the Great 

 Lakes show. It is certain that they have been subjected to the same 

 tremendous abrading agency. There are some explanations of the bowl- 

 der clay that appeal to local glaciers, on the flanks of distant highlands, 

 for the polishing of these lost blocks, but that deny anything but aqueous 

 agencies for all the phenomena that we find here. It is not easy to see 

 how these Corniferous limestone bowlders, thoroughly striatedand polished 

 as they are, can be made to match with such a view. 



An interesting fact in this connection, also, is the great number of the 

 peculiar spherical concretions of the Huron shale in the Drift of the 

 county. They abound in both divisions — viz., the unstratified and the 

 stratified. Scarcely a half dozen cubic yards of drift can be moved with- 

 out unearthing, one or more of these interesting bodies. They are often 

 partially decomposed, and almost always perish speedily after being 

 brought to the air. Their geological association and also their structure 

 will be remembered. They belong in the Huron shale, and are inter- 

 stratified with the thin and perishable layers of that formation. They 

 themselves are hard and heavy, as they generally contain a notable 

 quantity of iron in some combination. The shale would be the first ele- 

 ment, of course, to succumb to the glacial agencies, while these concre- 

 tions would prove, often, as well able to resist them as even the firmest 

 rocks of the north. It is to be noted, that the great numbers of these 

 bodies indicate the destruction of an immense body of the shale. This 

 fact matches well with others that have already been recognized in our 

 State geology. There is reason to believe that the Huron shale once 

 stretched across from its present outcrop to the Indiana line in an un- 

 broken sheet. Its destruction would supply a large amount of clay, quite 

 similar to that which we find in our unmodified drift-beds. 



The bowlder clay is generally blue in color, as one of the names by 

 which it is oftenest designated, implies. There are, however, blackish 

 streaks or pockets frequently seen in it, the color of which is due to veg- 

 etable substances intimately intermingled with it. These beds have the 

 appearance of soils, pre-glacial in origin, that were pushed forward and 

 worked over by the glacier as it advanced. 



More interesting specimens of vegetable growth are not lacking in the 

 bowlder clay. It is not an uncommon occurrence to find the trunks, 

 branches, or roots of trees deeply buried in it. Most of these specimens 

 seem water worn, or at 1 ast there is no indication of their having grown 

 where we find them. In this respect they are very different from the 

 buried tree-growths reported in Highland county (Report of Progress, 

 1870), and in other portions of southern Ohio. A true inter- glacial soil and 



