472 NATURAL HISTORY. 



auriferous sands of the Rhine is estimated at .$30.000,000. 

 Africa yields annually 4.500 pounds, troy, $850,000, and 

 Southern Africa 1,250 pounds, $235.000. The mines of 

 South America and Mexico were estimated by Hum- 

 boldt to yield annually about $11,500.000, Brazil 

 17.500 pounds troy; and between 1790 and 1830 Mex- 

 ico produced $31,250.000 in gold, Chili $13,450,000, 

 and Buenos Ayres $19,500,000, making an average an- 

 nual yield of $16,050.000. 



The mines of the Southern United States have pro- 

 duced of late about a million of dollars annually. Local- 

 ities of gold mines in the United States are Virginia, 

 North and South Carolina. Georgia, and Eastern Ten- 

 nessee. The California gold mines are ^mostly alluvial. 

 The gold is found in the gravel and sand of the valleys 

 and beds of streams leading from the Sierra Nevada into 

 the adjoining valleys of the Sacramento and San Joa- 

 quim. Pebbles of quartz abound in this region, also 

 magnetic iron. Native gold is also found disseminated 

 through quartz and talcose rocks, confined to veins ; the 

 precious grains may sometimes be seen shining in the 

 cavities of the quartz rock, or sparkling on a surface of 

 fracture. Plate 32, fig. 1. 



Native Platinum seldom occurs in crystals; most 

 commonly in flattened or angular grains or irregular 

 masses : is never pure, but combined with more or less 

 of the rare metals, as iridium, palladium, etc., besides 

 copper, iron, and chrome. Luster metallic : color steel- 

 gray, opaque ; ductile and malleable. H. = 5.0 to 6.0. 

 G. = 17.1 to 17.9. Pure platinum is the hardest and 

 most infusible of all metals, and is, besides, the heaviest 

 body known ; its weight, when freed from all alloy, being 

 G. = 21.0. It occurs with native gold in brown iron- 



