SOUECE OF THE OEE. 91 



brought about in it, such as the formation of iron pyrite and the concen- 

 tration of gold and silver in that mineral from the porphyritic mass. 

 Moreover, although it is not certain that the gold, silver, and lead in the 

 mines in its immediate neighborhood were derived from this rock, yet the 

 amount of gold, silver, and lead it contains, and the transformation it has 

 undergone, render it a possible source of these metals in the ore of the mines 

 of Adams Hill. The mines of Adams Hill, which are mentioned in another 

 portion of this memoir, are many of them noted for the large proportion of 

 gold to silver found in their ores. As regards the mines of Ruby Hill, 

 which are separated from those of Adams Hill by an intervening belt of 

 shale, it cannot be stated as anything more than a possibility that their ore 

 was derived from the decomposition of the quartz-porphyry. 



Granite as a possible source of the ore. — It has already been mentioned (page 12) 

 that granite probably underlies the sedimentary rocks of Ruby Hill, and 

 perhaps those of the whole district. This rock has but one small outcrop. 

 It has been carefully assayed, but only a trace of silver and no gold has 

 been discovered in it. The only place where specimens could be obtained 

 was on Mineral Hill, and they were all much decomposed. It is nowhere 

 exposed in the underground workings, although bowlders resembling granite 

 have been found in the quartzite near the bottom of the Richmond shaft. 

 It is only natural to expect that this decomposed granite should show very 

 little of the precious metals even if the undecomposed rock originally con- 

 tained perceptible quantities. Investigations which have been made of mas- 

 sive rocks carrying gold and silver have always shown that the decom- 

 posed varieties were invariably poorer in these metals than the unaltered 

 rock, except where enriched by infiltration. 



source of the ore in Prospect Mountain. — With reference to the deposits of Prospect 

 Mountain, which are almost identical with those of Ruby Hill, it can be 

 stated that although there is no quartz-porphyry or any other massive 

 rock carrying perceptible quantities of gold and silver in its imme- 

 diate vicinity, yet there is no proof that such rocks do not exist in depth 

 in or near the ore-bearing formation, and that, as such rocks have been 

 found on Adams Hill in connection with ore deposits, it is possible that 

 they may have been the source of the ore in that region as well. 



