] SUBTERRANEAN GASES. 33 



to be influenced by the direction of the wind. The investigations 

 concerning this subject are not yet concluded. It may be said, how- 

 ever, that a sudden lowering of the barometer seems to be the most 

 important factor. Upon such a fall the gas issues in great volumes, 

 but decreases when the barometer remains steadily low for several 

 days. The gas is often very heavy, filling lower parts of drifts and 

 winzes like water, and cases are reported in which it has actually been 

 bailed from a shaft. Its temperature is somewhat higher than that 

 prevailing in the mine under normal conditions. 



It has practically no smell or taste, but small quantities of it easily 

 produce effects of suffocation. Miners working in places where this 

 gas is mixed with the air soon experience various forms of physical 

 distress, and several fatal accidents have been caused by men entering 

 drifts and winzes filled with it. 



The characteristics of the gas seemed to point to carbon dioxide, 

 and it is generally so termed. Preliminary determinations of carbon 

 dioxide by a portable apparatus yielded percentages which seemed far 

 too small in comparison with the effects of the gas examined, and led 

 to the belief that some other substance was present. Samples were 

 then collected and analyzed. The analyses showed the gas to be a 

 mixture of nitrogen with about 20 per cent carbon dioxide and a small 

 amount of oxygen. 



The occurrence of these exhalations over a large part of the ore- 

 bearing area is of much interest. They certainly increase in quantity 

 with depth, and it is to be feared that in some cases they may seriously 

 affect mining operations. The evil has proved very difficult to cope 

 with. Ventilation alone has rarely proved efficient, and the only 

 practicable remedial measures appear to be cementation of drifts at 

 particularly bad places and working the mine under air lock at a pres- 

 sure slightly exceeding the normal. 



The origin of these gases can not reasonably be sought in any such 

 explanation as the oxidizing of sulphides and accompanying absorption 

 of oxygen. We believe that they represent the last exhalations from 

 the throat of the extinct Cripple Creek volcano. 



FUTURE OF THE DISTRICT. 



To predict the future yield of any mining district is no easy task; 

 the conditions under which most ores are deposited are as yet too 

 imperfectty understood, and the deposits themselves are usually too 

 erratic in form and distribution, to give certitude to such predictions, 

 even when these are based upon a careful study of the history and 

 present condition of a district. Nevertheless, it is part of the duty of 

 the geologists who have officially investigated the Cripple Creek dis- 

 trict to interpret to the best of their ability the bearing of ascertained 

 Bull. 25405 3 



