254 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
tem which does not freely communicate with the more open rocks and fissures of the 
western half of the district, as is shown by the failure of the drainage tunnels to 
rapidly unwater them. 
In the western part of the district, extending as far east as Eclipse Gulch and 
Bull Hill, gas began to be encountered as depth was attained. In the Wild Horse 
mine it was found at a depth of 1,200 feet, in others at from 500 to 800 feet below 
the surface. It may issue uniformly from the country rock, chiefly from a porous 
and fractured breccia, as in the Ophelia tunnel, or directly from partly open vein 
fissures, as in the Elkton. In many cases, as at the Moose and Conundrum mines, 
it pours out along basic dikes in more or less shattered rocks. Again it may locally 
issue from fractured granite near the contact with the igneous rocks, as in the El 
Paso mine. In places, at periods of low barometer, it will break out and possibly 
entirely fill a mine which at other times is free from it. It may issue almost con¬ 
tinuously from a certain place in a drift, even with good ventilation, producing a 
local barrier of bad air. 
PHYSICAL CHARACTERISTICS AND COMPOSITION. 
The gas is colorless and without noticeable taste or odor. It is stated, how¬ 
ever, that it sometimes, when very strong, appears as a bluish haze If this is cor¬ 
rect, it is no doubt due to its being saturated with water gas, as is the usual case with 
the carbon dioxide of the Victorian deep alluvial mines. It is a heavy gas, normally 
filling the lower part of winzes and drifts up to a horizontal plane defined by the 
sudden extinction of the candles. Apparently, however, its weight is not an unfailing 
characteristic, for it is reported from some places—the Last Dollar mine, for 
instance—as accumulating in the roof of the crosscuts. When the breast of the 
Ophelia tunnel was examined (p. 269) the acetylene lamps barely burned, but no 
difference whatever was noticeable in the amount present on the floor and in the 
back of the tunnel, which is 8 feet high. The percentage of carbon dioxide measured 
was only 0.68. The temperature of the gas is without doubt higher than the normal 
temperature of the mines. This is well shown by the fact that in the nonventilated 
breast of the Ophelia tunnel the temperature is + 58° F. when gas issues, and only 
+ 54 F. on days when gas is absent. In the Conundrum mine the temperature on 
the 600-foot level was + 62° F. when the drift was filled with gas, and only -f- 53° F. 
when, with a higher barometer, the gas had subsided to a point where it filled only 
the winzes. As shown on page 270, the normal increment of temperature in the dis¬ 
trict as measured in gas-free mines is 1° F. in 60 feet. This corresponds to the lower 
temperatures given above, while the higher figures would give an abnormally rapid 
increment. 
Where no determination of moisture is required, the gas can be collected in a 
large bottle, say an acid bottle holding about 2 or 3 liters, simply by filling it with 
water and emptying it in the locality to be sampled. The two samples from the 
Conundrum mine were collected in tins manner. A more accurate apparatus was 
used in the Elkton mine, where the gas issued from a fissure in the roof of the drift. 
It consisted of two 2-liter bottles, stoppered and connected by a rubber tube pro¬ 
vided with pinchcocks. A long rubber tube reached up from the dry gas bottle 
to the fissure and was inserted in it as far as possible. The other bottle was filled 
