CHAPTER XIV. 



TIMBERING IN THE EUREKA MINES. 



The method of timbering.— The methods employed in timbering shafts and 

 drifts in the mines of the Eureka District do not differ in any material re- 

 spect from those employed in other regions of the Pacific slope, while the 

 system adopted for preventing the caving of excavated ore chambers origi- 

 nated on the Comstock, and has been described by Mr J. D. Hague." It is 

 now in use in all districts of the West where the size of the ore bodies has 

 made it necessary to depart from the methods usually employed in small 

 lodes. The framing of the timbers at Eureka, however, presents some par- 

 ticularities to which it is desirable to call attention. 



Physical nature of the different formations.— As a rule, the limestone CODQpOSJng the 



ore-bearing zone requires but little timbering where it is penetrated by 

 drifts and winzes, and it is only where it has been crushed to a powder that 

 workings of this character need to be kept open by timbers. Where drifts 

 have been run along the line of the quartzite and limestone contact, tim- 

 bering is almost always necessary, as the quartzite and accompanying clay 

 scale off and in the course of time fill up the drift. Drifts in the quartzite 

 itself stand better, but, nevertheless, often require timbers, especially where 

 there is much water. There are but few workings in the shale, but if there 

 were, much timbering would no doubt be required to keep the ground open 

 for any considerable length of time, as is shown by the cross-cut through 

 the lower belt of shale on the 1,200-foot level of the Locan shaft. The 

 "crawling" of the shale in this instance is much increased by the water 

 present in it at this level, and it has been necessary to retimber the cross- 

 cut several times within a few months. Shafts and winzes in the limestone 



"Exploration of the Fortieth Parallel. Vol. III. 



