604 Transactions of the American Institute. 



below another. "Whenever a drift strikes a large deposit of rich ore, 

 the latter is removed until the drift is enlarged into an immense 

 cavern. From the conformation of the lode, however, the vertical 

 shaft and the ramifying drifts of the levels starting therefrom cannot 

 fulfill all the requisites essential in the workings. The ledge of silver- 

 bearing rock lies in an inclined position, having a dip or slope of forty- 

 five degrees toward the east, a hard syenite below and a softer 

 material above it. When the shaft reached the depth of 1,150 feet it 

 struck the syenite. Instead of piercing this refractory and worthless 

 rock by continuing the shaft vertically, and then running drifts hori- 

 zontally, to get back to the ore, the manifestly better course was taken 

 of running an inclined tunnel following the angle of the ledge and 

 communicating with the bottom of the shaft. This sloping tunnel, 

 like the horizontal ones in the levels, has a railway track, but the car, 

 instead of being run by hand, is worked up and down by a wire rope, 

 extending up the shaft to the surface, and then, like those that operate 

 the cages, over a sheave to a reel which is operated by a separate 

 engine. The driving shaft which communicates motion from the 

 engine to this last indicated reel has also an indicator for showing 

 the position of the car at any portion of the incline, there being fur- 

 ther provided the whole length of the latter a wire that works a 

 signal at the surface, so that the car can be stopped, if necessary, at 

 any point. A general idea of the subterranean workings in the mines 

 may therefore be had by imagining a timber-lined shaft or well 

 extending down 1,150 feet into the earth, with horizontal tunnel 

 radiating from it at different depths, ramifying in various directions 

 through the rock, and sometimes expanding into huge caverns where 

 the ore has been found of unusual richness and in large quantities. 

 From the foot of the shaft extends a tunnel of about the same 

 diameter as the shaft itself, and sloping down at an angle of forty-five 

 degrees for a distance of 200 feet or thereabout. As the mines are 

 all located on the same lode, they are, of course, divided only by 

 imaginary lines, their drifts connecting so that parties may pass 

 directly from one mine into another, the ledge being honeycombed 

 by the tunnels. The caverns caused by the excavations, as just men- 

 tioned, must not be considered clear spaces hollowed out within the 

 rock. It is true the ore is all removed, but in its place heavy timbers, 

 closer and stronger than any railway trestle work, are framed in to 

 prevent the fall of rock, which, were this precaution neglected, might 

 at any moment involve whole gangs of miners in destruction. As 

 the excavations are carried deeper, the want of fresh air is more and 



