STATE GEOLOGIST. 307 
CHAPTER V. 
ORIGIN OF OIL AND GAS, AND THE GEOLOGICAL CONDI- 
TIONS UNDER WHICH THEY ARE FOUND. 
I. ORIGIN OF OIL AND GAS, 
Few questions relating to Economic Geology are more generally asked 
than that of the origin of oil and gas, and few are more difficult to answer. 
In fact it is impossible to state with certainty at the present time how these 
fuels have been formed. Nevertheless, because of the great interest, the 
subject will be reviewed here. 
Petroleum and natural gas are intimately associated. Wherever oil 
is secured there gas also is found, and as is well known, it is the expansive 
force of the gas which produces flowing wells. As the gas escapes the 
force weakens and the well ceases flowing. Generally where natural gas is 
found in large quantity oil also exists, or is near. This is often well illus- 
trated on anticlines, gas being found at or near the summit of the arch 
and oil farther down the slope. However, oil is not always associated with 
gas. Thus the great gas -fields of central Ohio are not associated directly 
or indirectly with oil. In fact the Clinton formation has nowhere been 
proven to be an important producer of oil. As has already been reported 
in this volume, a small pool of oil has been found in the Clinton in the 
northern part of Vinton county and one well has been secured in this forma- 
tion in Perry county, but these wells are many miles from the gas field. 
In the Homer field oil is still more conspicuously absent, no wells having 
yet been reported. Examples of a similar nature might be cited from other 
parts of Ohio and also from additional states, and so it may be regarded 
as certain that petroleum is not a necessary accompaniment of natural gas. 
Considered from the chemical standpoint oil and gas are closely re- 
lated, and where the oil has an*unusual composition the gas of the same 
field is likely to be characterized in a similar manner. An illustration of 
this is found in the oil and gas of the Trenton limestone fields where the 
sulphur which is so striking a constituent of the oil is found in the gas also. 
In those fields where sulphur is not found in the oil it has not been reported 
in the gas. 
From the intimate association of oil and gas in nature and from their 
chemical relations it seems certain that both have been derived from the 
