SHALER: EXPULSION OF GASES. 
91 
each of these cases the territories affected were underlaid by porous 
materials which are known to contain large amounts of organic 
matter in a state of decomposition. In the marshes near Newbury, 
Mass., the layer of decaying material may well be some score feet 
thick. In the upper part of the Mississippi Delta and in the Tertiary 
and Cretaceous beds which border and underlie it the strata are im¬ 
perfectly unconsolidated and are the seat of much chemical action, 
which produces carbon dioxide and other gases. The same is the 
case with the strata about Charleston; there, as the evidence 
obtained from bored wells shows, the rocks abound with imprisoned 
gases, the products of decomposition, in sufficient quantity to give 
their water a considerable ascending- force when a well is bored 
o 
into them. It seems that the evidence above adduced, which is 
perfectly consonant with much other to the same effect, is sufficient 
to warrant the supposition which appears to have been tacitly 
adopted, that these earthquake fountains are primarily due to the 
presence in the disturbed strata of imprisoned gases which by the 
shock are made free to take on an upward motion ; we may there¬ 
fore turn to the question as to the way in which these movements 
are brought about. This task is best begun by looking more closely 
at the facts as they were recorded in the Charleston earthquake. 
In the region west of Charleston after the notable shock of 1884 
I had a chance to examine, with some care, the distribution of the 
fountain pits about two years after they were formed. They were, 
though somewhat affected by weathering, still in an excellent state 
of preservation, so that their positions and original shapes could be 
clearly determined. On a level portion of the sandy plain adjacent 
to a railway track these fountain pits showed a curious and instruc¬ 
tive distribution. Next the track over an area of almost an acre in 
extent, but much longer than wide, the ground to the depth of 
about four feet had been cut away, the earth having been removed 
for use in making an embankment. In this surface there were a 
score or more of the pits ranging in diameter from one to three feet. 
On an equal area on the neighboring higher ground, the number of 
depressions was less than half as great as on the surface of the 
lowered held. It may be said that the amount of vegetation of the 
higher ground, though greater than on the lower, was so slight that 
there was practically no danger of overlooking the sites of the 
fountains. 
Owing to the fact that the original notes and a detailed map of 
