258 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
air might have been included in it and that a gradual absorption of oxygen might 
have taken place. On the other hand, it might be contended that the continued 
exhalations of the volcano would long ago have driven out any included air. If 
this is true, the larger part of the nitrogen must be of magmatic origin. 
REMEDIAL MEASURES. 
In many mines no particular inconvenience is experienced by these gases, 
owing to the fact that they issue in relatively small amounts or to exceptional 
facilities for ventilation. At other places the gas has proved a most difficult 
problem. At the Moose mine strong blowers were used with indifferent effect; 
experiments were made both by exhausting the gas and by forcing in fresh air. 
At times of low barometer all measures fail at this and other mines, as the gas 
pours out in irresistible volumes. The very next day the mine may be free from it. 
Many different remedies have been suggested. Where carbon dioxide is the 
only gas to contend with, chemical means, such as absorption by lime, have been 
proposed, but these may without hesitation be put aside as impracticable. No 
doubt powerful blowers would in many cases dilute the air sufficiently, but the 
expense would be a serious matter for many mines. Exhaust fans would appear 
to be less suitable. In the Conundrum mine and in some mines in Gilpin County 
steam pipes have been introduced in the workings, and the condensing steam is 
said to have given considerable relief at times. The only way in which the steam 
acts is probably by promoting a circulation of the air. A blower should give 
better results. In some cases particularly bad places in the drifts have been 
cemented or lined with sheet metal. This is no doubt an excellent remedy as far 
as it goes. It would seem that the only really effective way of combating the evil 
would be to maintain, in emergencies, by means of powerful blowers and properly 
arranged air curtains, a pressure in the workings which would slightly exceed the 
normal atmospheric pressure. This is called the ‘‘plenum” system of ventilation, 
and has been successfully applied in coal mines and in the alluvial mines of Vic¬ 
toria, the objectionable gas being carbon dioxide in the latter case. At least this 
method could be applied to certain parts of the workings. Considerable expense 
and some difficulties would no doubt be connected with it. In case of failure of 
the blowers it would no doubt also increase the danger of the men working in the 
mine, but in some cases it would seem to be the only possible remedy. 
CARBON DIOXIDE AND NITROGEN IN OTHER MINING DISTRICTS. 
Carbon dioxide (carbonic acid) is known to occur at many places, although 
in metal mines it is somewhat rare. In coal mines it may develop by explosion 
of fire damp or by exudation from coal seams; in metal mines the explosives used 
generate a slight amount; locally it may be due to the action of oxidizing sulphides 
on carbonates. The lead mines of Pontgibaud, France, contained much of this 
gas; also those of Alston Moor and Foxdale, England. Carbon dioxide is fre¬ 
quently present in the Thames district on the Hauraki Peninsula, on the north 
island of New Zealand, and here often interferes with the working, especially during 
periods of low barometer. 0 The Hauraki veins intersect late Tertiary andesite. 
a Park, James, The geology and veins of the Hauraki gold fields: Trans. N. Z. Inst. Min. Eng., vol. 1, 1897, p. 23. 
