12 BEREA GRIT OIL SAND IN CADIZ QUADRANGLE, OHIO. [bull. 198. 
well. The other factors sire porosity of the reservoir rock and degree 
of water saturation, and their importance has not been sufficiently 
recognized heretofore. While these can be absolutely determined 
only by the expensive method of drilling, an exact solution can not be 
reached until they are determined. A careful study of all existing 
data derived from wells already drilled in the region will throw light 
upon the structure and will enable some forecast to be made concern- 
ing the probable condition of the oil sand in a given localit} T where no 
drilling has been done.- It is fully realized that all predictions in 
regard to oil and gas are of uncertain value, but it is believed that 
those here made are conservative, and that they will at least prevent 
much useless expenditure. 
PETROLEUM. 
Character and origin. — There has been much discussion, and differ- 
ent theories have been advanced, concerning the genesi of petroleum. 
A review of these discussions would occupy much space; it is suffi- 
cient to make a simple statement of those conclusions which have been 
reached from the consideration of established facts and which are 
accepted by a majority of the leading geologists. 
Petroleum is a complex mixture of hydrocarbons, belonging chiefly 
to the paraffin series, which are designated under the general formula, 
C n rL n+2 . It varies in color from pale straw yellow through reddish 
and dark brown to black. The specific gravity or density varies 
from 0.777 to 0.007, or from 50° to 16° of the Baume scale. It is 
probably derived from organic matter, both animal and vegetable, 
contained in the shales and limestones of the Silurian and later ages. 
Oil in Pennsylvania. — With the discovery of oil in western Penny 
sylvan ia, on Oil Creek, a new industry opened. The earlier develop- 
ments were confined to the lower lands along the streams, and for some 
time the higher or hill land was not considered available as oil terri- 
tory. In a short time it was found that the elevation of the surface 
of the ground had little or no relation to the oil supplies beneath. It 
was noticed, however, that the productive territory followed lines 
running in a northeasterly and southwesterly direction, with a bear- 
ing of about 45° from true nortn. This gave rise to the 45°-line 
theory, and a great deal of prospecting was done by extending explo- 
ration from a developed pool on a bearing of 45° to the northeast or 
southwest. As development proceeded toward the south the bearing 
lines of productive territory gradually changed until, instead of a 45° 
line, a bearing of 22° from true north or south seemed to lead to the 
most profitable extensions. 
With the development of the natural-gas industry, Mr. W. A. Ears- 
man and other operators noticed that the most productive wells were 
