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ORIGIN OF ROCK PRESSURE OF NATURAL GAS. 157 
lished in the American Manufacturer, May 27, 1887, | threw out a few 
suggestions as to the cause of rock pressure, and these suggestions I 
afterwards expanded into a more extended statement, in the sixth vol- 
ume of the Geology of Ohio, p. 96. Prot. I. C. White reminds me that 
he suggested an explanation in the journal named above at an earlier 
date than either of those given. 
The men who are engaged in the practical development of gas and 
oil fields make great account of rock pressure. It is the first fact that 
they inquire after in a new gas field. They appreciate its importance 
in whatever utilization of the gas they may propose, knowing that the 
distance of the markets that they can reach and the size of the pipes 
that they can employ are entirely dependent upon this element. These 
practical men, so called, are as is well known, among the most ven- 
turesome of theorists, and a question like this would not be likely to 
be left unanswered by them. A certain rough correspondence that 
exists between the depth and the rock pressure of wells is made of great 
account in explanations that they offer. In other words, the pressure 
is supposed to be due to the weight of the overlying rocks; and next 
to this we find among them the expansive force of gas the favorite ex- 
planation of the phenomenon. 
In the paper of Prof. Lesley, already referred to, the learned author 
suggests the two possible explanations of rock pressure already named, 
and to this he adds a third, viz, hydraulic pressure; but he adds this 
explanation only to reject it as a true cause of the phenomenon under 
discussion. The absurdity of the more commonly received explanation 
of rock pressure, as due to the depth of the well—in other words to the 
weight of the overlying country—he sets in such clear light in his dis- 
cussion that no further consideration of this is required on the part of 
those who are open to reason. Until we can prove, or at least render it 
probable, that the gas rocks have lost their cohesion and that they exist 
at the depths of storage in a crushed or comminuted state, no explana- 
tion can be based upon the weight of the overlying rock in aceount- 
ing for the force with which the gas escapes from its reservoirs when 
they are penetrated by the drill. Prof. Lesley throws the whole weight 
of his authority in favor of the view that the gas “ produces its own 
pressure like gas generated by chemical reaction in a closed vessel.” 
This explanation certainly leaves something to be desired, for it fails to 
account for the most significant and important facts in this connection, 
viz, the difference of rock pressure in different localities and at differ- 
ent depths. To accept it, brings us no advantage whatever beyond the 
satisfaction that we may feel in having an answer at hand that can be 
promptly given to a troublesome inquiry. 
For my own part, I have felt certain for more than two years that the 
rock pressure of gas in the Trenton limestone of Ohio and Indiana is 
hydrostatic in origin, and I have published a number of facts that 
seem to me to give support to this view. I find that some sagacious 
