108 MINING INDFSTEY, 



The method employed in timbering drifts or tunnels of the Comstock 

 mines is generally similar to that in use in other mining districts. The tim- 

 ber, however, is all square, varying in size from 8 to 13 inches. Ordinary 

 working drifts, such as those connecting the main shaft with the vein, are 

 about 5 feet wide in the bottom, 4 feet wide in the top, and 7 feet high. They 

 are usually timbered with vertical sets or frames, consisting of two posts, a 

 cap and a sill, or spreader. In the Savage these posts are 7 feet 2 inches 

 high, the cap 3 feet 9 inches, and the sill 4 feet 9 inches long. These sets 

 are placed from 2 to 6 feet apart, according to the nature of the ground. 

 They are covered on the outside with lagging, which is likewise varied accord- 

 ing to the condition just named, consisting sometimes of 6-inch scantling, in 

 pieces 5 or 6 feet long, and placed several inches apart ; sometimes of 3-inch 

 or 4-inch plank placed close together, inclosing both sides and top, and some- 

 times the bottom. Lagging, consisting of light scantling, placed several inches 

 apart, is often preferred in heavy, swelling ground, as the pressure breaks in 

 the pieces of scantling before affecting the stronger timbers of the tunnel-sets; 

 by picking down the intruding clay and relieving the pressure, the more expen- 

 sive timbers are saved. String pieces, usually of square stuff, or 3 inches by 

 4 inches, are laid in the bottom on the sill-timbers and shod with flat iron 1^ 

 inches wide by ^-inch thick, to serve as track for the drift-cars, and a footway 

 of 2-inch plank is laid between the rails. 



Figs. 3 and 4, on Plate IV, illustrate the method of framing the tunnel- 

 sets. Fig. 4 is the ordinary form ; Fig. 5 is a style of timbering in use in the 

 lower level of the Gould and Curry, in passing through very heavy ground. 

 In the cases illustrated, the lagging consists of plank placed closely together. 



The following statement, furnished from the books of the Gould and 

 Curry, gives the details of expense in driving and timbering one of the tun- 

 nels at the first station of their shaft, 225 feet below the surface, at mouth of 

 shaft, and 1,465 feet in length: 



