ORIGIN OF ROCK PRESSURE OF NATURAL GAS. 161 
districts has been reached than the law now stated, viz: The rock pres- 
sure of Trenton limestone gas is due to a salt-water column, measured 
from about 600 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 600 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 towards 
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 be- 
yond the limits I have named. Iam 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: 
(1) 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“cave in” or “blow up” after the gas is withdrawn from them.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 porus 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 that nature will not fail to perpetually maintain or perpetually 
renew the supplies which we find so delightfully adapted to our com- 
fort and service. So far as we are concerned it is certain that nature 
has done about all that she is going to do in this line. Jn her great 
laboratory a thousand years are as a single day. 
(3) No doctrine could exert a more healthful influence on the commu- 
nities that are enjoying the inestimable advantages of the new fuel than 
this. If it were at once accepted it would add years to the duration of 
these precious supplies of power. The ignorant and reckless waste 
that is going on in the new gas fields is lamentable. The worst of it 
comes from city and village corporations that are bringing the gas 
within their boundaries to give away to manufacturers whom they can 
induce on these terms to locate among them. To characterize the use 
of a million feet of natural gas a day, in a single town, for burning com- 
mon brick, for example, or in calcining common limestone, there is a 
good word at hand, viz., vandalism. 
(4) If this doctrine of the rock pressure of gas is the true one, the 
geologists who have to deal with the subject and the communities that 
have found a supply owe it to themselves to keep it prominently before 
the people who are especially interested. They may make themselves 
temporarily disagreeable thereby, but by just so far as they convince 
those that are interested, they lengthen the life of these precious sup- 
plies. 
H. Mis. 334, pt. 1——11 
