32 RESURVEY OF CRIPPLE CREEK DISTRICT. [BULL. 254. 



trict must be so modified as to exclude a certain part on the eastern 

 side, comprising the mines about Independence on the east side of Bull 

 Hill and those on Battle Mountain and in the town of Victor, in which 

 the effect of the El Paso tunnel is slight. The Findley, Hull City, 

 Vindicator, and Golden Cycle mines about the town of Independence 

 seem to occupy a separate drainage basin, probably divided from the 

 main area by masses of relatively impermeable rock. 



The Portland, Stratton's Independence, and the other mines near 

 Victor occupy another drainage basin. Of these the Gold Coin and 

 the Stratton's Independence have shafts below the level of the El Paso 

 tunnel, and their pumps have probably drained the surrounding terri- 

 tory to a considerable extent. The influence of the drainage tunnel 

 on the Portland mine is a question upon which opinions differ. 



The subject of the drainage of the Cripple Creek mines has been 

 actively studied in late years, and valuable contributions to the subject 

 have been made by Mr. Victor G. Hills and others, who have shown 

 that the water can be tapped, without prohibitive expense, down to an 

 elevation of 7,500 feet, or 1,300 feet below the El Paso tunnel; for 

 this depth a tunnel 3 miles long would be needed. On account of the 

 great porosity of the rocks it is not probable that the next thousand 

 feet below, the El Paso tunnel level will show any great diminution in 

 the amount of water stored in the rocks. 



SUBTERRANEAN GASES. 



During the earlier years of Cripple Creek no unusual amount of 

 mine gases was observed, but, as the shafts and workings deepened, 

 several properties began to experience much annoyance and even 

 serious interference with work, often in spite of vigorous measures 

 for ventilation. These gases appear to issue chiefly from the breccia, 

 especially where it is of porous and loose texture, but they sometimes 

 flow from partly open vein fissures in such quantity that a light held 

 up to the fissures is immediately extinguished. Thus far the mines 

 on Battle Mountain and those of the Golden Cycle, Vindicator, and 

 Isabella groups have suffered no inconvenience, but most of the mines 

 west of this line have had more or less trouble with this subtle and 

 insidious enemy. At least one mine has been forced to close down 

 entirely, and several others are often obliged to abandon work for 

 days. Sometimes the amount of gas issuing is small, and ordinary 

 ventilation will carry it away; again it may issue in large volumes 

 and practically fill the mine for some time. In other mines the gas 

 persistently hangs at certain places, forming barriers which can be 

 passed only with difficulty. The outflow of gas is unquestionably 

 related to barometric fluctuations, though it is usually locally reported 



