618 KANSAS CITY REVIEW OF SCIENCE. 



In the same way, the gold at the Black Hills is proved to be pre-Silurian, 

 since the Potsdam sandstone which abuts against the Archean nucleus of the hills 

 in places contains rolled fragments of the Archean rocks, and gold washed from 

 them in such abundance as to form rich mining ground — the so-called cement 

 deposits of that region. The distribution of gold from the Archean rocks has 

 probably been constantly going on from the Silurian age to the present day. 

 This is shown in the almost universal dissemination of gold through the drift of 

 New England, New York, Ohio, etc., where the superficial materials have been 

 largely derived from the Canadian highlands. In Ohio, gold is found in the 

 drift clays, sands, and gravels, and locally in as great quantity as in the poorer 

 placers of California. There is little doubt that the mechanical sediments derived 

 from the wear of the Archean rocks all contain gold, and since it .has been proved 

 that gold exists in sea-water, it has probable impregnated all the organic marine 

 sedimentary rocks as well. In the subsequent metamorphism of some of these 

 strata it has been concentrated in such a way as to produce auriferous quartz 

 veins rich enough to be worked. 



From these facts it will be seen that there is no geological age which can be 

 called the age of gold. It existed in the oldest rocks known, and from them and 

 their derivatives, more modern rocks, it has been, and is now, being constantly 

 distributed by both mechanical and chemical processes. Even some of the igne- 

 ous rocks of the western country are said to contain minute quantities of gold ; * 

 and this is not surprising, if, as is supposed, much of our volcanic material is a 

 fused condition of sedimentary rocks. 



GOLD IN FISSURE-VEINS. 



As is well known, gold is a frequent constituent of the fissure-veins of the 

 Far West. The ore of the Coms^^ock vein has yielded about forty-seven per cent 

 of gold and fifty-three per cent of silver ; and it is probable that one half of the 

 so-called silver veins contain gold in sufficient quantity to be of practical value. 

 In some true fissure-veins, gold is the only valuable ingredient, but more gener- 

 ally it is associated with several other metals. The Revenue Mine, at Tusca- 

 rora, Nev., contains silver in the form of arsenical and antimonial sulphide, and 

 gold in iron pyrites frequently crystalized lining cavities. At Eureka, the ore 

 occurs in chambers, which were originally filled from a solution issuing through 

 fissures from below and deposited as argentiferous galena and auriferous pyrites, 

 the silver and gold being in nearly equal proportions. In the great veins of 

 Bingham Canon, and at the Cave Mine, near Frisco in Utah, the combination is 

 the same, and, as at Eureka, the sulphides have been decomposed to a spongy, 

 rusty gossan. At the Bassick Mine, in Colorado, gold exists free, or in combina- 

 tion with tellurium and associated with zinc, copper and iron. In all these, and 

 many other cases which might be cited, the gold has been brought up in a hot 

 solution impregnated with mineral matter far below, and deposited as the tem- 



* For example the basalt of the Snake River lava plain and according to Prof. J. J. Stevenson, the trachyte 

 of Colofado. 



