MINING. 253 
very tightly by the sand collected between them. In large 
sluices, wooden riffle-bars are worn away very rapidly—the 
expense amounting sometimes, in very large and long sluices, 
to twenty or thirty dollars a day; and in this point there is an 
important saving by using the stone bottoms. They are used 
only in large sluices, and they generally have a grade of twelve 
dr fourteen inches to the box of twelve feet. 
§ 185. Hydraulic Mining.—After the board-sluice, with its 
various adjuncts of riffle-bars, stone bottoms, copper plates, 
and so forth, the next instrument of importance in the gold- 
mining of California is the hydraulic hose, used to let water 
down fen a considerable height, and throw it under the press- 
ure of its own weight against the pay-dirt, which is thus torn 
down, broken up, dissolved, and carried into the sluice below. 
The sluice is a necessary part of hydraulic mining. The hose 
is used, not to wash the dirt, but to save digging with shovels, 
and to carry it to the sluice. 
The hydraulic process is applied only in claims where the 
dirt is deep and where the water is abundant. If the dirt 
were shallow in the claim and its vicinity, the necessary head 
of water could not be obtained. Hydraulic claims are usually 
in hills. The water is led along on the hill at a height varying 
from fifty to two hundred feet above the bed-rock, to the claim 
at the end or side of the hill, where the water, playing against 
the dirt, soon cuts a large hole, with perpendicular or at least 
steep banks. At the top of the bank is a little reservoir, con- 
taining perhaps not more than a hundred gallons, into which 
the water runs constantly, and from which the hose extends 
down to the bottom of the claim. The hose is of heavy duck, 
sometimes double, sewn by machine. This hose when full is 
from four to ten inches in diameter, and will bear a perpendic- 
ular column of water fifty feet high; but a greater height will 
burst it. Now, as the force of the stream increases with the 
height of the water, it is a matter of great importance to have 
the hose as strong as possible ; and for this purpose, in some 
claims, it is surrounded by iron bands, which are about two 
