602 GEOLOGY OF OHIO. 
ust below the horizon of the Buena Vista stone lies the Berea 
shale, a bed of highly bituminous and very fossiliferous black shale, 
ranging from 15 to 30 feet in thickness. Its bituminous composition 
makes it a source of petroleum, which rises into the sandstone courses 
that lie above it. This is the source of one of the worst impurities of 
the Buena Vista stone. When followed under cover it is found loaded 
with petroleum or with tar, which seems not only to disfigure the stone but 
to weaken it to some extent; and other impurities in the stone are 
masked for the time by this bituminous matter. The oil-bearing stone 
is tolerated only in rough, heavy work. Some of the stone contains 
sulphide of iron, which, on exposure of the weather, becomes oxidized 
to the sulphate and goes into combination with compounds of alu- 
minum, and appears on the surface of the stone as a white efflorescense 
which has the characteristic taste of alum. Grains and nuggets of 
pyrites appear in the shales associated with this sandstone, but are not 
very perfectly visible to the naked eye in the city ledge (the name now 
applied to the stratum proper of Buena Vista stone). The rock is 
quarried by channeling and wedging in the same manner as in the quar- 
ries of the Berea grit in northern Ohio. No stone is extracted for the 
market during the winter months, but this time is occupied in removing 
the cap-rock and in channeling. The behavior of the material when 
properly selected is apparent in a number of’ important structures in 
Cincinnati, and that of the unselected material may be seen in the 
custom-house and other buildings in Chicago. ‘The material has also 
been used with good and bad results ina number of other cities and 
towns, including Louisville, Kentucky, Pittsburgh, Pennsylvania, and 
Detroit, Michigan. 
CARBONIFEROUS.—The Carboniferous conglomerate (Sharon con- 
glomerate of the Second Geological Survey of Pennsylvania) furnishes the 
only important building stone in Portage county. This formation in 
Ohio geology is commonly called “the Conglomerate.” 
In Franklin, Mantua, and Nelson townships, where it is well.seen, 
it is a coarse, drab-colored sandstone, in places thick set with quartz 
pebbles from the size of a pea to that of an egg. It.is quarried in these 
localities to a small extent for local purposes. 
At the quarry of Messrs. Case & King, in Windham township, it is 
finer, whiter, and more homogeneous, and answers quite well for archi- 
tectural purposes. It is rather too coarse for fine work, but it is strong 
