PRECIOUS METALS. 573 



to date have not thoroughly tested any of the deposits. The quantity already 

 mined has been insignificant, and the indications do not augur well for future 

 discovery, but the possibility of procuring these as extras in the mining of 

 baser ores gives at least a little inducement to persevere in the work of ex- 

 ploration. Such expensive methods as trial shafts and drifts are unnecessary, 

 and their proper location is a very puzzling problem in numerous localities; 

 but judicious prospecting with the diamond drill may lead to information of 

 very great importance. The mam difficulty in this work is to select points 

 for boring which shall yield the most conclusive evidence, and this choice of 

 site must be entrusted to experienced persons familiar with the geology of 

 the region as well as with the mechanical details involved in the boring pro- 

 cess. It is not enough that the one in charge be capable of excavating 

 adroitly, for if he be not also alive to the meaning of each change in the rock, 

 and practically acquainted with the geologic structure of the region, his re- 

 sults, if at all valuable, will prove very costly, as has already happened in 

 Texas more than once. 



The relations of gold and silver in nature are such that they frequently ap- 

 pear in identical situations, although there are enough differences in the 

 modes of occurrence to make one abound sometimes in places where the 

 other is not present in commercially important quantities. For this reason 

 each metal is here treated by itself. 



1. GOLD. 



As remarked in the writer's report for 1889, there are three principal situ- 

 ations in which we may expect to detect its presence by tests of suitable ma- 

 terial if gold exist in the district in notable proportions. The examination of 

 these possible sources of supply has been materially extended in 1890, so that 

 the conclusions here announced may fairly be regarded as final concerning the 

 likelihood of obtaining this metal in workable quantities, unless deeper work- 

 ing should disclose more solid ore bodies. The probabilities are not in favor 

 of such results. 



The outcrops to which especial attention has been given are: 



(a) The multitudinous dikes, veins, and bosses of quartz which traverse a 

 considerable variety of the rocks of different ages, more particularly those of 

 ancient origin. 



(b) Quartz and other vein fillings occurring in fault fissures and joint 

 crevices. 



(c) Bands, pockets, and segregations of pyrite and special minerals. 



