ENGINEERING. 387 



the current of this prospective rich and abundant traffic to 

 our own ports, to the advantage of American manufacturers. 

 At the time of this writing, the steamer Mercedita had 

 sailed from Philadelphia with a large number of engineers 

 and laborers, and the first load of supplies and machinery, 

 for the scene of operations. This vessel is to be followed 

 by others, and monthly communication between the base of 

 supplies and the Madeira will be kept up. 



THE SUTRO TUNNEL. 



The latest advices indicate that the great tunnel into the 

 Comstock silver lodes is gradually approaching completion. 

 At the time of this writing it is officially announced that the 

 tunnel-heading had penetrated into paying ore, and had been 

 driven a distance of 18,400 feet into the mountain. This 

 would bring the tunnel, as near as may be estimated, to 

 within less than one hundred feet of the great combination 

 mining-shaft, which, when reached, will practically complete 

 the undertaking and determine its value. The following 

 statements of the nature and history of this enterprise may, 

 in view of the above facts, be of interest: 



The object of the Sutro Tunnel is to facilitate mining op- 

 erations in the Comstock lode, the difficulties and expensive- 

 ness of which are very serious. The mines have reached a 

 depth of from 1000 to 2500 feet; and the cost of pumping to 

 keep the workings free from water entails an annual expense 

 of $2,000,000 or $3,000,000. This fact, and the circumstance 

 also that the temperature in the deeper portions of the work- 

 ings reaches as high as 120, render mining operations enor- 

 mously expensive. These difficulties the Sutro Tunnel is 

 designed to obviate by tapping the workings at a depth of 

 about 1S00 feet from the surface, creating, therefore, a new 

 surface for ventilation and drainage at the 1800-foot level 

 of the mines, by which it is expected (as the water will be 

 drained off, by the natural flow through the outlet provided, 

 to the depth of 1800 feet) that the cost of pumping will be 

 largely reduced, and that the means of ventilation which it 

 will provide will so far reduce the temperature as to enable 

 the miners to work in comparative comfort. In addition to 

 these obvious advantages which it is expected to realize 

 from the tunnel, there are others of considerable commercial 



