632 HYDRAULIC MINING. 
LITydraulie Mining. 
What is called hydraulic mining—a system substantially 
identical with that described in an interesting way by Pliny 
the elder, in Book XX XV. of his Natural History, as practised 
in his time in the gold mines of Spain*—is producing important 
geographical effects in California. Artificially directed cur- 
rents of water have been long employed for washing down and 
removing masses of earth, but in the Californian mining the 
process is resorted to on a vastly greater scale than in any other 
modern engineering operations, and with results proportioned 
to the means. Brooks of considerable volume are diverted 
from their natural channels and conducted to great distances 
in canals or wooden aqueducts,t and then directed against 
hills and large level surfaces of ground which it is necessary 
to remove to reach the gold-bearing strata, or which them- 
selves contain deposits of the precious mineral.t Naked 
hills and fertile soils are alike washed away by the artificial 
torrent, and the material removed—vegetable mould, sand, 
gravel, pebbles—is carried down by the current and often spread 
over ground lying quite out of the reach of natural inunda- 
tions, and burying it to the depth sometimes of twenty-five feet. 
An orchard valued at $60,000, and another estimated at not less 
* Thave little doubt that the hydraulic mining in Gaul, alluded to by Dio- 
dorus Siculus, Bibliotheca Historica, v. 27, as merely a mode of utilizing the 
effects of water flowing in its natural channels, was really the artificial method 
described by Pliny. 
+ In 1867 there were 6,000 miles (including branches) of artificial water- 
courses employed for mining purposes in California. The flumes of these 
canals are often of shect-iron, and in some places are carried considerable 
distances at a height of 250 feet above the ground.—Raynmonp, Mineral Sta- 
tistics west of the Rocky Mountains, 1870, p. 476. 
} The water is sometimes driven through iron tubes under a hydrostatic 
pressure of several hundred feet, with a force which cuts away rock of con- 
siderable solidity almost as easily as hard earth. In this way of using water, 
the cutting force might, doubtless, be greatly augmented by introducing sand 
or gravel into the current, 
