SHALER: EXPULSION OF GASES. 
95 
take part in the nearest npgoing procession which by the relief of 
pressure afforded the inducement to the movement. As soon as the 
column of water impelled by the gas, in the manner of a stream from 
a soda fountain, begins to move up any joint fissure, it would in 
incoherent rocks at once begin to break up the adhesions of the 
material, driving the debris before it, and thus produce a better pas¬ 
sage for the movement. So far as the expansion of the gas in the 
portions of the strata near the channel served to disrupt the ad¬ 
hesions of the grains it would favor the widening of the pipe, and 
the consequent freer uprush of the combined gas and water. 
Quite independent it may be of earthquake action, vertical shafts 
of gas-impelled springs are frequently produced whenever in very 
wet and incoherent strata conditions are instituted which essentially 
resemble those which we have been discussing. Thus along the 
banks of the greater rivers of the Mississippi System where thick 
deposits of alluvium exist, it is easy to find between high and low 
water-mark springs which emerge through vertical, cylindrical vents, 
which often have a diameter of an inch or more and which may be 
sounded to the depth of several feet. Through these vertical wells 
the water comes forth impelled by the gases formed by the decom¬ 
position of the organic matter contained in the alluvium; in many 
cases the stream rises with a considerable amount of ascensional 
force. It often drives before it a great deal of mud, forming there¬ 
from a cone singularly volcanic in its aspect. In their larger forms 
these cones are the so-called “ mud lumps ” of the Mississippi Delta, 
in which region the slight swerving action of the stream permits the 
ejections to accumulate until they may form hillocks having a height 
of ten feet or more. I am convinced that a large, perhaps the 
larger, part of the springs which emerge through considerable thick¬ 
nesses of incoherent strata owe the formation of the channels which 
lead to the surface to the action of gas pressure. In many cases I 
have found that such ordinary springs contain a certain amount of 
gas; it is reasonable to suppose that before their channels were 
opened to the surface the amount of this gas was much greater than 
it is after the flow had flowed for a long time. If space allowed, 
mention might be made of instances in which such springs had been 
observed suddenly to break forth, for a time spouting in a way that 
indicated a considerable amount of gas pressure. Such facts indi¬ 
cate that many of the superficial deposits of the earth are in condi¬ 
tions which favor the discharge of their waters under the impulse of 
