SURFACE GHOLOGY. 39 
limestone, said to be nearly equal in bulk to a cube twenty feet on a 
side. A ereat number of bowlders, scarcely smaller than these, are 
mentioned in the notes of the Geological Corps, but these are sufficient to 
show the power of the transporting agent. Smaller bowlders are some- 
times found in immense numbers over a limited space. Near Euclid, 
in Cuyahoga county, they are so thickly strewn over a field of several 
acres as to resemble a large herd of sheep and cattle. Hven in southern 
Ohio they are locally very numerous. Prof. Orton mentions a belt of. 
these bowlders, two or three miles wide, between Dayton and Eaton, 
where they are so thickly set as to make the cultivation of the soil 
almost impossible. Here the bowlders are almost exclusively Canadian 
metamorphic rocks, among which a granite, with rose-colored felspar, a 
eray gneiss, diorite, and silicious slate, are the predominating varieties. 
Along the highlands of the divide we occasionally see blocks of consider- 
able size, which have been torn from some neighboring ledge, and among 
the smaller rounded bowlders found on and south of the divide, a large 
number are derived from indigenous rocks, but the greater part of the 
larger bowlders strewed over the surface are of foreign origin. 
Very few of the surface bowlders show any striation or planing, such 
as is seen in those of the bowlder clay. This is a distinction that has 
an important meaning; for so large a number of the bowlders in the 
glacial clay (where they have been transported by glaciers) are planed 
and scratched, that the absence of such markings from the surface bowl- 
ders is pretty good evidence that they have had a different experience. 
We may, therefore, conclude that the striated bowlders have been trans- 
ported beneath glaciers, and that the 
rounded and unscratched bowlders CoNCRETION FROM DRIFT GROUND OFF 
have not. With the great limestone Een 
bowlder of Huron county are many 
of smaller size, which are very much 
scratched and worn. These rest on 
the surface of the Huron shale, and } 
we can hardly doubt that they have co aS 
been transported and left where} | | 
found by a glacier moving from the \ “335 
north. In the vicinity of these lime- 
stone bowlders a spherical concretion 
from the Huron shale was found, of 
which one side is planed off as 
smoothly as it could be done by art. Whether it was held in the glacier, 
or in the shale, when the grinding was done, is somewhat uncertain; 
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