16 ANNUAL REPORT 
We may say, therefore, that ferruginous shales; provided they are 
sufficiently low in alumina and magnesia, do not contain too much con- 
cretionary iron and are not too hard, are well suited as cement materials. 
The limit of the ferric oxide content may be placed at Io per:cent. 
In the consideration of these shales we must not overlook the fact 
that if they are too hard they are not the most suitable material, and in 
such a case one should try to find an area containing some of the weathered 
shale. The hard shale should be selected only if neither the clay pro- 
duced from the shale by completed weathering nor the soft shale between 
the shale clay and the hard shale can be had. 
The table* of analyses on page 77 will show the composition of some 
Ohio ferruginous shales which might become available. 
A typical ferruginous shale when examined by the rational method 
of analysis gave the following mineral analysis: 
Per cents. 
Clay Substance ren orm. ties eee Mee a ee ee 62.27 
QU Arta Sige ee Pion oe re Se RE ee RL eee ZOROS 
Heldspathicidetrivustenenn rine reer nearer 12.07 
Owing to the high content of iron these shales, of course, produce 
dark colored cements, but many of them are very suitable for cement 
making purposes as far as the chemical composition is concerned. 
Silicious Shales—We have in Onio no large areas of distinctly 
silicious shales, but many local deposits are available. Often where a 
transition from shale to sandstone is found the shale as it approaches the 
stone becomes more and more silicious. If this silicious dilution is fine- 
grained, the material becomes extremely valuable for cement making 
purposes; in fact we might say that it would be the ideal of a cement 
clay. In reality, however, the sand addition is frequently too coarse 
erained and the resulting shale is not any better than any clay mixed 
with sand. The locating of a suitable silicious shale is therefore a matter 
of local conditions; for instance, we might find a high bank of shale of 
which only a part is silicious, a strata only a few feet in thickness. 
Rather extensive deposits of silicious shales are found between the 
horizons of the Bedford and Cuyahoga shales. The Berea grit, a sand- 
stone, frequently carries 8 to Io per cent. of alumina and possesses the 
shale structure, making it a valuable material for cement manufacture. 
Though the Berea grit does not always show this structure, it invariably 
accompanies the Bedford shale, being found above the latter. The grit 
is usually very fine grained and when burnt assumes a red color. Judicious. 
mixing and grinding together of the Berea grit and Bedford shale would 
in many cases produce a most suitable basis for the making of Portland 
cement. This seems to the writer to be a point well worth looking into 
*Prof. Hdward Orton, Jr., Ohio Geological Survey, Vol. VII, Part I, p. 182. 
