MANNER OF DEPOSITION. 105 



Preponderance of evidence in favor of the substitution theory. Weighing the evidence Oil 



both sides of the question, it appears that a large part of the ore was 

 brought into its present position by substitution, while it seems impossible 

 to demonstrate that any part of it was deposited in pre-existing caves. It 

 is highly probable that all the ore was deposited by substitution, and that 

 future developments will effectually establish the fact. There is no reason 

 for believing that, if the physical conditions favorable to the deposition 

 continue below the water level, deposits of ore will cease to be found below 

 that point. 



Age of the ore. — In the Ruby-Dunderburg mine, on Prospect Mountain, 

 there is a rhyolite dike similar to that of the Jackson and Phoenix. In all 

 of these mines ore has been found in contact with and below the rhyolite 

 in the limestone, but has never been found on the opposite side of it. This 

 fact alone would not necessarily prove that the dike is older than the ore 

 bodies, for these might occupy their present relation to it in consequence 

 of a fault; but the manner in which the ore is deposited on the rhyolite, 

 showing no signs of having been disturbed, and the fact that the rhyolite 

 does not in any place contain inclosed fragments of ore, though it often 

 contains country rock, go to prove that the eruption occurred before the 

 deposition of the ore and that it did not fault the ore bodies. Another 

 fact tending to prove the subsequent formation of the ore is the extreme 

 decomposition of the rhyolite through the ore-bearing region, which was 

 no doubt brought about by chemical action attending the deposition of ore. 



Although it has not been established beyond doubt that the rhyolite 

 eruption caused the upheaval which made the main fault on Ruby Hill, yet 

 it is extremely probable that such was the case. It has been shown that 

 this fault was the last dynamic disturbance of any importance that occurred 

 in this region, and nothing is more natural than to connect it with the latest 

 volcanic outburst in its neighborhood. If the Ruby Hill fault was formed 

 by the rhyolite eruption it is likely that the rhyolite was injected into it at 

 the time of its occurrence. The ore solutions seem to have entered the 

 limestone through the main fissure after its formation and not simultaneously 

 with it. And it may be inferred that the ore solutions owe their genesis to 

 the solfataric action following the ejection of that eruptive rock. As the 



