CLAY DEPOSITS. 659 
height that the coals exhibit. But such standards of comparison render 
but little service, because a fire clay is of little value unless of good’ 
quality. Itis not accessible by cheap means'for the common uses and is 
not so well adapted to those uses as still poorer clays ; and the formations 
at best now yield, in only a small extent of their territory, any suffi- 
ciently pure clays for the higher uses. 
There are undoubtedly valuable districts of clay in Ohio yet un- 
tested and undeveloped. The geological questions as to the source and 
formation of the clay seams are not by any means well wrought out. 
A deposit of fine-grained clay always lines the depression in which 
peat bogs grow; its fineness and color show that it must have been de- 
posited from nearly still water, perhaps in so fine a state of division 
that the water which carried it would have been clear to the eye. This 
much is found in common with coal seams, that a fine-grained clay 
underlies them also. The similarity in the origin of peat and coal are 
unquestioned, so that the causes which produce our fire-clay veins are 
still operating to-day. ‘The coal deposits are miles across and hundreds 
of miles in linear extent, yet the clay floor is much more constant in 
volume than the coal. The quality changes constantly, however, and it 
has no fixed character over any large area. With the questions of 
formation, the distinction between flint clays and plastic clays again 
arises. Itis hard to understand how clays can be found in the same 
seam, side by side, mutually replaceable and running in varying propor- 
tions in each cubic yard, which are chemically and physically in sharp 
contrast with each other. 
The valuable coal seams of Ohio are mainly in the lower meas- 
ures, and the clay deposits worked are wholly confined to that group. 
The following geological section of the Lower Coal Measures has 
been prepared to indicate the names, order and geological horizon of our 
clay deposits, previous to a description of each important bed. It is, of 
course, ideal, covering so large a range of territory as it does, yet it will 
serve as an accurate general guide. It is drawn to scale, but the inter- 
vals are not given; the latter are given in chapter I, with sufficient 
accuracy for the various districts of the State. The elements which 
serve as marks from which to identify the clays are mainly coals, but a 
few limestones and ores are important. These formations and the clays 
are named in the column nearest the section. In the other column the 
facts are grouped concerning the clay deposits. 
