80 
OIL AND GAS; OHIO, WEST VIRGINIA, PENNSYLVANIA. 
ture with a greenish tinge. Its upper portion is crowded with fos¬ 
sil crinoid stems and brachiopods. I rom the abundance of crinoid 
stems this bed is often spoken of as the “ crinoidal ” limestone. In 
its greatest development it consists of two benches which are fos- 
siliferous, but the upper bench carries the larger number of fossils. 
Two small coal beds are closely associated with the limestone. The 
upper bed, which is from 1 to 20 feet above the limestone, is not 
more than 1 foot thick. The lower bed is more constant and usually 
maintains a distance of 20 feet below the limestone, although here 
and there it occurs directly beneath that bed. This coal is in many 
places 1^ to 2 feet thick and breaks from the bed in long rectangular 
blocks. 
CAMBRIDGE LIMESTONE. 
About 95 feet below the Ames limestone is another limestone of 
similar composition and appearance. It probably contains a greater 
number of brachiopod shells, but the fragments of crinoid stems are 
much less abundant. This bed is commonly known as the Cambridge 
limestone, from its occurrence at Cambridge, the county seat of 
Guernsey County, Ohio. It was positively identified at only two 
points in the Steubenville quadrangle. 
MAHONING SANDSTONE. 
The lowest member of the Conemaugh formation is the Mahoning 
sandstone, which is rather coarse and of a light yellowish-gray color. 
It varies from 30 to 60 feet in thickness and has some value as a 
building stone. It is also a good water-bearing stratum when under 
cover. In places it is rather prominent, but not persistent, and in 
many localities it appears to be displaced by shale. 
ALLEGHENY FORMATION. 
The Allegheny formation includes all the rocks from the top of 
the Upper Freeport coal to a horizon about 100 feet below the Lower 
Kittanning coal. This group of strata is important economically 
because of the coal and fire clay contained in it. In the area investi- 
gated it carries five coal beds, each of which is mined at some place 
in the area, although as a rule not more than two are mined in any 
one locality. This formation also contains a few beds of limestone, 
but generally they are thin and inconspicuous. 
FINLEY COAL. 
The Finley coal of the Steubenville quadrangle is believed to be 
equivalent to the Upper Freeport coal of Pennsylvania, though this 
is not considered proved. It varies greatly in thickness, changing 
