TIMBERING. 



155 



bers are similar in their general features to those in use on the Comstock. 

 It is only as regards the manner in which they are framed that they differ, 

 and even in this respect the differences are but slight. 



When an ore body is encountered in driving a drift, it is usual to place 

 the first sill across the drift, laying the ties parallel to the drift. This is 

 done to retain as wide a space as possible for the passage of the car, the 

 sills being longer than the ties. In carrying up the timbering the timber 

 which forms the cap of a lower set becomes the sill of the set above it. 

 The same is the case with the ties. In beginning a stope the sills often 

 consist of a long piece of timber in which the posts are mortised at their 

 usual distance apart. As each set is i-aised the caps are covered with two- 

 inch plank, and in this way floors are constructed. The spaces between 

 the floors and timbers are filled with waste, and thus a compact mass is 

 formed from one side of the ore chamber to the other and from the bottom 

 to the top, which takes the place of the ore removed, and which is capable 

 of sustaining the enormous pressure exerted by the surrounding rock. The 

 timbers are wedged and braced against the limestone walls of the cham- 



Fig. 9. — Richmond framing. 



bers, so that the whole stands solid. It is customary to fill in with waste, 

 as opportunity offers, the absence of that peculiar "crawling" ground so 

 -common on the Comstock obviating the necessity for immediate filling. 



