Crosby.] 514 [March 7, 



is favorable to the view that the mineralizing process was mainly 

 hydrothermal, since the heated mineral waters would naturally 

 pass downward more freely than upward. 



Concerning the source of the gold in the Ruby Basin ores, two 

 opinions have arisen: (1) The gold was derived with the other 

 constituents of the Potsdam quartzite from the auriferous quartz 

 veins in the Archaean schists, the gold being sorted and concen- 

 trated by the waves of the Potsdam sea as by modern rivers. 

 This view is supported by the fact that gold has been found in the 

 basal conglomerate or cement beds of the Potsdam, even where it 

 is not associated with the igneous masses. But gold worn from 

 the Archaean veins by the Potsdam sea would naturally have been 

 deposited mainly or wholly at the bottom of the nearest slope or 

 hollow, and this would alwa3 T s insure its lodgment in the basal 

 layer of the Potsdam gravel and sand. The occurrence of free or 

 placer gold higher up in the Potsdam, say fifty feet above its 

 base, would involve the very improbable conclusion that the gold, 

 like the fine sand, had been carried by marine currents across sev- 

 eral or many miles of the sea-bottom. Certainly, there would 

 then be no tendency to concentrate the gold ; but it would be dif- 

 fused with inappreciable thinness through the whole body of the 

 formation. 



(2) The gold has been derived directly from the porphyry, 

 and dates, in its present position, only from the metamorphism of 

 the Potsdam beds. This view explains the occurrence of the gold 

 in precisely the positions in which it is found ; and is supported 

 b}- the very important fact that numerous assa3's have proved that 

 the porphyry is always auriferous, sometimes containing, as I 

 have been informed by reliable assayers, over half an ounce of 

 gold per ton. Although the exact condition or form of the gold in 

 these ores remains to be determined, it is quite certain that it exists 

 in almost infinitesimally small particles, precisely as if it had been 

 deposited by chemical means. It seems fair to suppose that it was 

 introduced by the same solutions which deposited the interstitial 

 or secondary silica converting the sandstone to quartzite. This 

 chemical explanation also accords with the occurrence of silver 

 ores in these contact deposits in the eastern part of the Ruby Ba- 

 sin ; for these could not possibly have been transferred by any 

 mechanical means from the Archaean to the Potsdam. 



Whether the gold of the Homestake and other mines situated in 



