SILVEE MINING IN COLOEADO. 595 



concerning the experience in this kind of work, in the tunnel just referred to, 

 at the Terrible mine. 



The air compressor of two cylinders, each 12 inches diameter and 16 

 inches long, only one of which is required for the present work, is set up at 

 the mouth of the tunnel, and driven by an engine of 12 inches diameter. It 

 is capable of running two drills, but only one is used. The drill is worked 

 under a pressure of air of 35 to 40 pounds; strikes 300 blows per minute; the 

 drill is 14 inch steel, with If inch bit; the progress of the drill in the hole 

 averages 2 inches per minute; each drill, on the average, drives 30 inches 

 before needing to be sharpened; the machine is managed, at the heading of 

 the tunnel, by two men on each shift, who drill from six to eight holes per 

 shift, including the time required for charging and firing, the latter being done 

 by electricity, and for removing the broken rock; the force required at the 

 tunnel comprises six men, four of whom are drillmen and two engineers, be- 

 sides the smith, at the mine, who sharpens the drills. Labor costs $4 50 to 

 $5 per day, for shift of twelve hours. The average progress of the tunnel is 

 1^ feet per day of twenty-four hours. It is reported that the property of the 

 Terrible mine has been recently sold in England for $500,000. 



Brown. — Brown Mountain, on which the lode just described is located, has 

 been extensively prospected, and a number of valuable veins have been opened. 

 Among these the John Brown, U. S. Coin, Lilly, Roe, Mammoth, and others 

 have been developed considerably, and have produced some very rich ore. 

 The John Brown lode crops out on the hill-side, 300 or 400 feet above the 

 Terrible. It has a nearly parallel course, north 75° east, and dips almost ver- 

 tically, but slightly incHned to the south. The width of the vein is variable. 

 Where both walls are clearly defined they appear to be from two to five feet 

 apart; but the south wall is often difficult to distinguish, and as the filhng of 

 the vein is, to a large extent, granitic, or like the country-rock, it is not 

 always easy to define their position. Where cross-cut in one or two places the 

 vein is thought to be from 15 to 24 feet wide. The ore of this vein resem- 

 bles that of the Terrible in most respects, but is characterized by the occur- 

 rence of much more zincblende. This is the predominating mineral, and is 

 said to be argentiferous. With it is also mixed considerable galena, rich in 

 silver, and a small proportion of pyrites, with true silver minerals. These are 



