62 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
sufficient to “ cut” it, as it is called, — that is, to disintegrate and break it 
up, so that it can be moved by the current, after it has spent its force 
against the bank, down into the sluices.* Of course the arrangements for 
effecting this must be suitably adapted to the circumstances. In the first 
place there must be an ample supply of water; then a sufficient slope of the 
ground, with an unchecked outlet, so that the sluices may be laid in a suit- 
able position, and there be room for the “ tailings,” or material which issues 
from the end of the sluice, after leaving behind in the riffles the greater por- 
tion of the gold which it contained. It is owing to a happy combination 
of favorable circumstances that the system of hydraulic mining has been 
so successful on the slopes of the Sierra Nevada. That the peculiar set 
of conditions which makes hydraulic mining possible is not often met with 
is sufficiently proved, by the fact that this system, which seems so admirably 
adapted to the needs of the Californian gravel miners, has hardly been at all 
successful in any other region. It has been tried again and again in the 
Southern United States, with almost unvarying loss; and, even in Australia, 
where the mode of occurrence of the gold is in many respects so similar to 
what it is in California, there are few districts where the hydraulic method 
can be applied. 
The first great need of the hydraulic miner is an abundance of water, and 
with a considerable “head,” so that the stream may issue with sufficient 
velocity from the pipes. The conditions of rain-fall in the Sierra having 
been already explained, it will not be difficult to understand how an abun- 
dance of water may be secured for the miners’ use. But this cannot be done 
without extensive engineering operations, and the expenditure of a large 
amount of money. Extensive reservoirs must be constructed, by building 
dams across the outlets of the mountain valleys, so as to impound the water 
coming from the melting of the winter’s snow on the High Sierra, and the 
necessary canals —or ditches, as they are universally called by the miners — 
must be excavated to carry the water to the points where it is needed for 
use} The long, rapid, and rather uniform slope of the Sierra, in the miming 
districts, makes it possible almost everywhere to carry the ditches with such 
a grade and in such a position as to allow the water to be taken from them, 
at a sufficient elevation to give the necessary head at the point of working. 
* Where, as is often the case, the gravel is too solidly compacted to be readily “cut” by the pipes, 
powder is freely used to shake up the mass, which is then much more easily acted on by the hydraulic jet. 
+ See farther on, for examples of the mode of construction, extent, and cost of such dams and ditches. 
