HARMONY OF OBSERVATION AND CALCULATION. 93 



These figures seem to me to settle the question as to the origin of the rock 

 pressure of the gas in this formation. I feel sure that nicer determinations 

 of the facts involved as to altitude and depth would bring a still closer 

 agreement between columns four and five. I will ask you to note in par- 

 ticular the facts as to the St. Mary's and the St. Henry's wells. They have 

 practically the same depth, 1159 and 1156 feet; but there is a difference of 

 thirty-eight feet in the depth of the gas rock with reference to sea level. 

 There is a corresponding difference in the rock pressure of fifteen pounds, as 

 recorded. The difference in rock pressure due to this thirty-eight feet by 

 calculation is 13.8 pounds, or practically fifteen pounds. I presume that 

 column five is as near the truth in this particular as column four. The 

 gauge would quite certainly be reported 385 pounds if it lacked but one or 

 two pounds of that number. 



The Laws of Gas Production. 



The laws of gas and oil production and accumulation are coming to light 

 more clearly in the flat country of Ohio and Indiana than they have ever 

 done among the hills and valleys of the older Alleghany fields. As it seems 

 to me, no more important deduction from the new districts has been reached 

 than the law now stated, viz., The rock pressure of Trenton limestone gas is due 

 to a salt-water column, measured from about six hundred feet above tide to the 

 level of the stratum which yields the gas. The column can be conveniently 

 counted as made up of two parts, viz., a fixed length of six hundred feet 

 added to the depth of the gas rock below tide. 



If this explanation is accepted as satisfactory for Trenton limestone gas, 

 I venture to suggest that the fact will go a great ways toward rendering 

 probable a like explanation for rock pressure in all other gas fields ; but I 

 will not at the present time venture to extend it beyond the limits I have 

 named. I am aware of certain facts, or at least supposed facts, from the 

 older fields that seem difficult of explanation on this basis. 



There are a few obvious inferences from this law to which I venture to 

 call your attention in closing this paper : 



"J. There is no danger that the great gas reservoirs of to-day will "cave 

 in " or " blow up " after the gas is withdrawn from them. The gas will not 

 leave the porous rock until the salt water obliges it to leave by driving it 

 out and taking its place. 



2. This doctrine lays the ax at the root of all the optimistic theories which 

 blossom out in every district where natural gas is discovered, and especially 

 among the real-estate operators of each new field, to the effect thai Nature 

 will not fail to perpetually maintain or perpetually renew the supplies which 



