NEW YORK, FEBRUARY 23, 1894. 
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SOME RECENT WORK ON CLAYS.’ 
BY G. PERRY GRIMSLEY, BALTIMORE, MD. 
THE seventh volume of the Ohio Geological Survey, 
under the direction of Prof. Edw. Orton, which has just 
appeared, contains an extended and interesting chapter 
on the clay deposits and workings in that State. The 
work is primarily intended for the assistance of those 
actively engaged in this work, and many suggestions are 
given which will prove of great value; but here also will 
be found the only complete account of the process of 
manufacture of city paving materials. 
Ten years have passed since the last published work on 
Ohio clays; in this interval there has been great expan- 
sion in the industry, and new features have been intro- 
duced. At the present time there are over twenty-five 
distinct lines of clay manufacture, and in most Ohio 
leads. In the sewer-pipe industry it stands foremost in 
amount of ware and in possession of three of the largest 
factories in the world. 
Coal has always been regarded as Ohio’s great source 
of mineral wealth, but where this is removed clay deposits 
are found which are greater sources of wealth than the 
original coal. Thus the Ohio coal measures are now 
becoming the clay measures. 
The best clay must be free from calcium, iron and 
alkali bases, for if these be present they will act as 
fluxes, so destroying the clay as a refractory material. 
Since clay originates from minerals containing these 
elements, it is rare to find this high grade clay, and, when 
found, the deposits are most valuable. 
There is no true scientific classification of clays, but 
they are popularly divided into clays and shales; the 
latter originated in deeper water and very often show no 
plasticity. A high grade clay is composed of kaolin and 
silica, while the poorer grades in addition have the fluxing 
elements. 
It is found that nearly every coal seam is underlaid by 
a Clay, locally called fire clay. In most cases it is every- 
thing but a fire clay and is used only in potteries. 
Most of the true fire clays of Ohio belong to the non- 
plastic type. In this clay small microscopic bundles of 
rods are found, indicating incipient crystallization; it is 
thought the peculiar property of hard fire clay depends 
on this property, since there is no chemical difference 
between such a clay and a plastic one. 
The lowest clays worked in the State are found at the 
4Geological Survey of Ohio, vol, vii., part i. Columbus, Ohio, 1893, 
base of the Upper Silurian, but they are only of local 
interest. The first important series to be worked is the 
great mass of Devonian black and blue shales at Columbus 
used in the extensive sewer pipe industry. The best clay 
in quality is found in the sub-Carboniferous Sciotoville 
clay used for fire brick. 
The important clay industries of the State are based 
almost wholly on the coal measure clays and _ shales. 
Under and over the coal occur clay and shales. 
The first of the Ohio coals has a roof of shales, which 
forms the basis of one of the largest sewer-pipé and 
roofing tile works in this country, located at Akron. 
The Mercer clays, below the Mercer coals, are used in 
the manufacture of terra cotta and ornamental brick, 
while the Kittanning series.support a second fire brick 
industry at Mineral Point. 
In the Freeport horizon occur the clays and shales 
which are used so extensively in central Ohio for the 
manufacture of paving brick. 
It would be interesting to follow out the development 
in the different lines, if space permitted, but only the new 
enterprise introduced in the last few years into this 
country will be reviewed. This whole subject has been 
most carefully investigated and described by Mr. Edw. 
Orton, jr., in this report. 
Ten years ago shales were regarded as so much waste 
in the clay workings; now they are found to be of great 
value. 
The difference between paving brick and common 
brick rests on the fact that the elements of the former 
have reached a state of fusion, and so are chemically 
united; while in the latter it is more the physical union 
of adhesion. The true test is absorption, which would 
be nothing in a perfect paving brick. 
The clay must conform to certain conditions in order 
to yield a good paving brick. It must combine refractori- 
ness with fusibility and must be sufficiently plastic to be 
easily worked. The amount of iron present determines 
the color of the ware and smoothness of surface. 
An average of a large number of analyses shows the 
composition of a good paving brick to be 84.78 per cent 
clay and sand, 13.22 per cent fluxes. High heat is not 
required and if present ruins the product. 
These shales have lost their natural plasticity, which 
must be regained. This is accomplished by grinding the 
dry material to a powder and tempering this to the 
proper consistency by the use of water. 
The universal method of grinding in Ohio is by the use 
of a large revolving pan, with two heavy iron wheels 
moving in this. The clay is next carefully screened to 
varying fineness, usually the finer the clay the finer and 
more durable the brick. 
The value of the ware depends most of all on the fem- 
pering; this is accomplished at the least cost by means of 
