STATE GEOLOGIST. 315 
a supply of animal matter at hand, it seems altogether unnecessary to 
search for a source in some underlying formation. 
However when the remaining oil and gas rocks are examined, the 
conclusions reached are not so positive. Thus the great gas wells in the 
central part of the state are obtained in a thin stratum of sand stone of 
Clinton age. Samples of this rock are not easily collected, and hence 
there is very little positive evidence bearing on the question as to its having 
contained organic matter. Lying below the gas sand are a few feet of 
dark colored shales concerning which we have little information. Exam- 
ination of a few samp:es gave no evidence of an abundant fauna or flora. 
Below these in turn lie the Medina shales, having a thickness according 
to Orton ranging from 50 to 150 feet, and commonly a red color. They 
have been classed in the Ohio reports as generally non-fossiliferous. These 
could not have been the source of the great body of gas in the Clinton rock. 
The next formation met in descending the geological scale is the Cin- 
cinnati series consisting of shales and thin bedded limestones. These are 
very rich in animal remains, but the gas in question does not appear to 
have originated from such material, for the analysis already given shows 
the gas free from sulphur compounds. However, if there were not this 
objection we would still be confronted with a serious one—that of ex- 
plaining how the gas could reach the Clinton when lying between it and 
the Cincinnati series are many feet of shales. It has long been the custom 
of geolgists to have as a condition for the occurrence of a reservoir of 
gas, an impervious bed lying above the rock containing the fuel in ques- 
tion. This is usually shale, a rock which from its fine texture seems ad- 
mirably suited for the purpose. Now if a bed of shale lying above an oil 
or gas rock will prevent the ascent of these substances, the same kind of 
rock lying below will also prevent oil or gas from rising and reaching 
the formation which now acts as a reservoir for these fuels. Shales appear 
impervious, and hence oil and gas cannot have passed through them. This, 
of course, excludes the theory that oil and gas have been produced from 
rocks lying beneath those which now contain the fuels. However, where 
a bed of shales lies immediately below a porous rock, oil or gas might pass 
from the top of these shales into the overlying formation, but they could 
not pass from lower points in the shales into the superimposed rock. This 
view seems necessary but it does not simplify the main question—that of 
the origin of natural gas in the Clinton sand. It must be remembered, 
however, that if the absence of organic remains in the Clinton could be 
demonstrated, it would not prove that such remains never existed in the 
rock. Thus many of our limestones contain in places very little evidence 
of animal origin, the hard parts having been ground to a mud before the 
rock was cemented. Now if this is true of such material, it would be more 
