BLACK HILLS GEOLOGY. 297 



sediments, and to have been deposited from the erosion of the 

 Algonkian throughout a large portion of Cambrian time. This 

 gold has not, however, at any time been of economic impor- 

 tance (except in the basal conglomerates), and is interesting only 

 as related to the formation of other deposits. 



The Cambrian Siliceous Ores. 



The siliceous ores are perhaps the most interesting ore bodies 

 in the hills, and now outrank the Homestake properties in their 

 output. Their occurrence, history and treatment have been 

 set forth by F. C. Smith in an excellent paper on the subject. 

 Other papers are those ofF. R. Carpenter, W. P. Jenney, Persifer 

 Fraser and W. O. Crosby. 



Distribution. — The producing districts have been divided by 

 F. C. Smith into the northern connected area, which is essen- 

 tially that included in the map accompanying this paper, and 

 the Galena area. In the first are the ores carrying gold and 

 silver, and in the second those with gold, silver and lead. The 

 first area onl)^ will be considered here. 



The northern connected areas of Smith is roughly divisible into 

 four parts : 



1. Ruby Basin or Bald Mountain district. 



2. Portland or Green Mountain district. 



3. The Crown Hill district. 



4. Sheeptail Gulch district. 



I. Ruby Basin District. 



The Cambrian strata are most extensively exposed in the 

 vicinity of Ruby Basin and Bald Mountain, and therefore the ore- 

 bearing horizons have been most easy of access in this vicinity. 

 Consequently this district has so far attained the greatest de- 

 velopment. The number of mines which have been either oper- 

 ated, or are now in operation, is very large, and it has been pos- 

 sible to examine only a limited number of them in detail. 



The following properties may be cited as illustrative of those 

 which are, or have been, large producers : The Tornado, the 

 Annals N. Y. Acad. Sci., XII, December 8, 1899 — 19. 



