ON GOLD AND SILVER. 515 



deepest Australian mines are fonnd. In tlie Sandhurst district tliere are 

 twenty-nine shafts over 600 feet deep, twenty-three over 1,000 feet, two 

 over 2,000. The deepest is the Magdala mine (Ararat), the shaft of 

 which is 2,409 feet deep. 



A lode of the same average productiveness, however, may pay well in 

 the upper part, but may prove unremunerative in the lower part, the 

 actual yield of gold remaining the same. The general working expenses 

 are far less for shallow mines than for deep mines. The lode is decom- 

 posed near the surface, and is more easily worked ; the sulphides are also 

 decomposed and the gold set free. In deep mines the sulphides are not 

 decomposed, and there is an increased loss in stamping and amalgamating. 



The second great division under which native gold may be classed is 

 that of alluvial deposits, derived from the waste of rocks containing auri- 

 ferous veins. The old conglomerates already referred to belong to this 

 class ; but their interest is scientific rather than practical, because they 

 are too limited in extent to yield much gold, although generally woi-ked 

 for the metal where they occur. 



The great alluvial gold deposits of the world are of newer Tertiary age. 

 The older beds of California and Victoria are believed to be of about the age 

 of our English Crag ; but the evidence for this is by no means conclusive, 

 and they may be of later date. Their great antiquity, however, is proved 

 by — 1. Their vast extent and thickness; 2. The great sheets of volcanic 

 rock which cover them ; 3. The enormous denudation which the gravels 

 and the overlying sheets of basalt have undergone. 



The modern alluvial deposits have been derived from the waste of 

 these old Pleiocene (?) deposits ; the gold has thus undergone a second 

 concentration, and the gravels are often proportionally enriched. 



Alluvial deposits have hitherto yielded at least nine-tenths of the 

 world's gold ; in old times the proportion was higher. The enormous de- 

 velopments of gold-mining within short spaces of time, as in California 

 and Victoria in 1849-52, were entirely due to alluvial mining. 



In Russia, Siberia, and British Columbia almost the whole of the gold 

 now produced is alluvial ; but in Australia, the United States, and in South 

 America vein-mining is increasing as the alluvial deposits are becoming 

 exhausted. 



United States. — Previous to the discovery of gold in California gold 

 was produced in the United States in Georgia, North and South Carolina, 

 Tennessee, Alabama, and Virginia : the total production of these States 

 from 1804 to 1850 is estimated at ^15,172,300, Georgia and North 

 Carolina each producing over ^6,000,000. 



Before 1871 California stood at the head of the States in its output 

 of the precious metals, but from 1871 to 1879 this place was taken by 

 Nevada, in consequence of the immense development of mining in the 

 Comstock area. In 1880 (census year) Nevada fell to the third place, 

 having been passed again by California and also by Colorado, which then 

 ranked first. In 1884 Nevada fell to the fourth place, having then been 

 just passed by Montana, Colorado keeping its place at the top of the list. 

 In 1885 the produce of Montana went rapidly ahead, whilst that of 

 Nevada remained stationary. 



The occurrence of gold in California was known to the Spanish Jesuit 

 missionaries and to others, but it was not worked till 1848. So rapidly 

 were the placers developed that in 1849 the production was 8,000,000Z., 

 and in 1853 it I'ose to 13,000,000Z. Gold-mining began in Oregon in 



t I, 2 



