MINIXG PRODUCT OF COLORADO FOR iSSi. 619 



perature and pressure were reduced. The formation of this class of auriferous 

 deposit is weil illustra'ed by the Steamboat Spring, in western Nevada, where 

 hot water, flowing out through fissures produced by subterranean forces, is de- 

 positing a siHceous vein-stone, containing sulphides of iron, copper, oxide of 

 manganese, and metallic gold. There is little doubt that, in the great mineral 

 belt lying between the Sierra Nevada and the Rocky Mountains, where, in Ter- 

 tiary times, volcanic activity was exhibited on a grand scale — sedimentary rocks 

 upheaved and fissured in every direction, with great outflows of fused material — 

 hot springs, like the Steamboat, were everywhere busy, doing similar work. 

 Bursting out at different places and times, and flowing from different sources, the 

 solutions they carried and the ores they deposited varied greatly; but the methods 

 of accumulation, transportation, and deposition were essentially the same, namely, 

 the leaching of various rocks by steam and hot water under great pressure, by 

 which silica and sparsely-disseminated metals were gathered and driven toward 

 the surface, to be deposited as the pressure and temperature were reduced. Gold 

 collected in this manner was unquestionably taken into chemical solution, and in 

 the resulting vein deposits we find it in strings, scales, and irregular masses, often 

 beautifully crystallized and associated with other crystallized minerals which are 

 certainly chemical precipitates. 



We may sum up "the teachings of geology in regard to the genesis and destri- 

 bution of gold by saying : 



First. Gold exists in the oldest known rocks, and has been thence distribut- 

 ed through all strata derived from them. 



Second. In the metamorphosis of these derived rocks it has been concen- 

 trated into segregated quartz veins by some process not yet understood. 



Third. It is a constituent of fissure-veins of all geological ages, where it has 

 been deposited from hot chemical solutions which have leached deeply-buried 

 rocks of various kinds, gathering from them gold with other metallic minerals. 



Fourth. By the erosion of strata containing auriferous veins, segregated or 

 fissure, gold has been accumulated by mechanical agents in placer deposits, 

 economically the most important of all the sources of gold. — Engineering and 

 Alining Journal. 



MINING PRODUCT OF COLORADO FOR 1881. 



Boulder $ 535,482 ^Z 



Chaffee 100,000 00 



Clear Creek . ' 2,204,980 34 



Custer 608,549 37 



Dolores 125,000 00 



Fremont 14,535 5° 



Gilpin 2,150,700 00 



Grand 10,000 00 



V-39 



