] 74 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. 



the ores. While many geologists and many engineers believe that ore 

 deposition is not limited to any depth within human reach, others are of the 

 opinion that ore in considerable quantity usually occurs only within a mod- 

 erate distance of the surface. This question, however, cannot be satisfac- 

 torily discussed from a theoretical point of view until much more is known 

 of the chemical and physical conditions of ore deposition, nor as a matter 

 of observation until far more thorough explorations have been carried on 

 at great depths in mining regions. Some deposits have been followed to 

 an immense depth (over 3,000 feet) without any diminution in yield; and 

 if it were possible to gauge the erosion to which their croppings have been 

 subjected since their formation, these and others would very likely yield 

 more striking data. On the other hand, in many cases the search for ore 

 below a certain depth has proved futile, but such cases afford purely nega- 

 tive evidence. Explorations at considerable depths are extremely expens- 

 ive, and are rarely made on a large scale. It is consequently as yet im- 

 possible to say even of any single district that ore in paying quantities does 

 not exist below a certain level, though it is certainly true of some that no 

 indications of its existence have been found which would warrant the con- 

 tinuance of the search for it. 



That the various companies owning these mines are fully justified in 

 view of the former enormous production and the probabilities of finding 

 ore in prosecuting a diligent though expensive search below the levels as 

 yet reached seems to be beyond question. 



As regards the future of Adams Hill and adjacent country, not much 

 can be said; the mines have not been worked to any great depth or extent,, 

 and but few predictions can therefore be made in regard to them. 



