THE DECREASE OF GOLD. 505 



zas " ; but, besides these bonanzas, crevices contain no gold, and only 

 the hope of encountering them leads to their being worked. 



The places in which gold is found may be divided into the follow- 

 ing three classes auriferous ore, auriferous veins, and auriferous allu- 

 vium : 



The first group contains ore, rich in magnesium, interspersed with 

 gold. It is frequently found in the Ural Mountains. As a transi- 

 tion to the second class may be regarded the auriferous minerals, in 

 rock of volcanic origin, as it occurs on the west coast of South Amer- 

 ica atid in many parts of Brazil. The granite of the Erz Gebirge, in 

 Bohemia, which contains tin, is a similar formation. Interesting as 

 this class is, considered from a geological stand-point, it is of little 

 practical value to the gold miner. 



The next class consists of the auriferous veins, which are fissures 

 filled by hot springs, geysers, or volcanic eruptions. The gold is found 

 here together with silver, as in the case of the Comstock lode, in 

 Nevada, the gold deposits in Queensland and New Zealand, as well as 

 the mines near Kremnitz, in the Carpathian range, in Hungary. The 

 gold is sometimes found in them pure, sometimes mixed with silver, 

 copper, or sulphur. In the older volcanic veins the gold is not mixed 

 with silver, and bonanzas are never found in them. In many of these 

 veins, also, granite veins are encountered, and, although remote from 

 volcanic regions, it is presumed that the gold was carried up by the 

 granite. The celebrated " Mother lode " of California is a sample of 

 this kind. 



The third class is the gold-bearing alluvium. This alluvium (earth 

 washed down by rivers upon lower lands) has been produced by the 

 decomposition of auriferous rock, and the gold is found in grains and 

 lumps to the size of a hen's egg. It is a peculiar fact that the gold 

 found in these deposits is purer than that contained in the veins from 

 which it originated, nor is the formation of lumps and grains satisfac- 

 torily explained. The deposits of California, Australia, and Siberia 

 pertain to this group, which may again be subdivided into a. Depos- 

 its on the earth's surface, from which the gold is obtained by simple 

 washing ; b. Deposits which have been covered by subsequent inunda- 

 tions, and from which the gold has to be mined only by difficult work 

 and great expense. These old deposits in California are frequently 

 covered with basalt or lava, and are called " deep leads." They are 

 worked by the hydraulic system : the water is conducted through pipes, 

 and directed with full force against the soil, which is hereby converted 

 into a fluid mud, and passes in this condition through a long line of 

 sluices, set in zigzag, in which the particles of gold are deposited. 



The most remarkable deposits of this kind are to be found at Bal- 

 larat, Australia, where they are covered with four hundred feet of 

 ground and four layers of lava, which have come from a neighboring 

 volcano. These deposits are the banks and bars of former streams, 



