TIMBERING. 



157 



is impossible to determine with any certainty what may be its ultimate 

 course, and consequently how the timbers should be placed. It is, there- 

 fore, well to have a system of timbering which will be equally effective in 



pO^ 



Fig. 10. — Eureka framing. 



all directions. When all the pressure comes from above, which, however, 

 is rarely the case, it would be well to have the ends of the posts rest 

 directly on each other, not allowing the tenon of the caps to intervene. 



Matenai and size of the timbers. — The usual length of the posts is 6 feet between 

 shoulders ; that of the caps and ties 5 and 4 feet, respectively. The timber 

 used is pine from the Sierra Nevada. It is hewn 12 by 12, 10 by 12, or 

 10 by 10 inches square, and is of excellent material. The ties used in the 

 Richmond are 10 by 10 or 10 by 12 inches, as the case may require. In 

 the Eureka they are usually 12 by 12, though occasionally they are but 

 10 by 12 inches. Sets of timbers 10 by 10 inches are sometimes used 

 when the ground will permit of it and the ore bodies are small, but 12 by 

 12 inches for the posts and caps at least is the rule. 



The timbers are cut into the required lengths by circular saws, and 

 framed by hand. Split lagging and sometimes poles are used in the 

 drifts and small ore bodies where the heaviest timber and planking are not 

 required. 



