SUBTERRANEAN GASES. 
257 
On August 5, without change in barometer, the gas disappeared, and conditions 
continued good until August 24, the barometer remaining steady. From August 25 
to October 29 the barometer remained at 20.4 to 20.5, and some gas was present at 
intervals. On October 29, for the first time since July 13, the barometer sank to 
20.3 and more gas appeared. On December 15, 23, and 24 the aneroid indicated the 
low pressure of 20 inches, and the whole mine was filled with gas. 
Imperfect as they are, these data seem to indicate that the gas is influenced to 
a lesser degree by some factor besides the atmospheric pressure. If, as seems 
probable, the gases are of volcanic origin and given oil' by a cooling magma, the 
supposition that their pressure is subject to some such fluctuations as appear when 
the barometer is steady, as during the summer months, is not unreasonable. It is 
to be hoped that long-continued and more detailed records, which no doubt will be 
kept in the future at the mines where gas appears, will throw more light upon these 
important questions. 
ORIGIN OF THE GAS. 
Although carbon dioxide may be introduced in mines locally by many natural 
and artificial processes, and although the proportion of nitrogen likewise may be 
increased in places by some such chemical reactions as oxidation of pvrite or com¬ 
bustion of powder, it seems entirely out of the question to account for the mine 
gases at Cripple Creek by such explanations. There is very little timbering used 
from which carbon dioxide could form by decay; there is only a small proportion 
of carbonates and pyrite present in the ores and rocks compared to that in many 
other mines entirely free from gas. Moreover, the fact that practically no gas was 
encountered in the oxidized zone shows that oxidation can not have anything to 
do with its origin. The sudden influx of large volumes in some mines at periods 
of low barometer clearly shows that vast amounts of this dangerous gas are stored 
in the rocks; and as the evil in general increases with depth, it is evidently accu¬ 
mulated mainly below the present workings in the porous volcanic rocks, a con¬ 
clusion also borne out by the fact that the gas has a higher temperature than the 
normal mine air. 
Considering further that exhalations of gases composed of carbon dioxide, 
oxygen, nitrogen, and sometimes also sulphureted hydrogen always take place 
after volcanic eruptions,® and that they frequently continue for a long time after 
the cessation of the igneous outbursts, we believe that the mine gases of Cripple 
Creek represent the last exhalations of the extinct Cripple Creek volcano. If this 
is true, and the evidence in favor of it seems to be strong, the next question is to 
what extent the gases have a magmatic origin, or whether a part of them, at least, 
can be included air. That the carbon dioxide has the former origin will doubtless 
be admitted. That the mine gases collected contain a considerable amount of 
diffused air obtained during their ascent or in the workings is also probable. The 
question whether some of the nitrogen is of magmatic origin is more difficult to 
answer. If the breccia was formed by explosive action, as seems likely, and then 
consolidated in the large vent of the volcano, it is reasonable to suppose that much 
a Henri Moissan analyzed the gases in one of the fumaroles of Guadeloupe, West Indies, with the following result (Comtes 
Rendus, vol. 138, 1904, pp. 936-938): Sulphureted hydrogen, 2.7 per cent; carbon dioxide, 52.8 per cent; oxygen, 7.5 per cent; 
nitrogen, 36.07 per cent; argon, 0.73 per cent. 
