[August, 
448 A Description of the Process of 
projefted from the nearest and most convenient ravine, so 
that the starting-point on the bed rock towards the iace ot 
the ravine shall approach the centre of the material to be 
removed at a gradient of 1 in 10 to 1 in 30. The dimensions 
of such tunnel are usually 6 feet in width by 7 in height, 
and continuing in contact with the hard river-bed, for the 
greater ease of excavation, collection of gold, and conserva- 
tion of quicksilver amalgam. 
These tunnels vary in length from a few hundred ieet to « 
a mile, and some of the longer ones occupying from one to 
seven years in execution, at a cost of from 10 to 60 dollars 
per foot of frontage. The tunnel of the Blue Gravel Com- 
pany, with length of 1358 feet, cost in labour alone 70,000 
dollars, but it could now be driven for 35,000 dollars, as 
skilled labour is cheaper now than then. The grade in this 
tunnel is about 12 per cent, and the end of the tunnel is 
designed to be 170 feet of elevation, and leaching to a point 
beneath the surface of the gravel which is being operated 
upon, and where a shaft or incline is sunk to or through 
the bed rock or gravel, until it intersects the tunnel. The 
objeCt of this laborious operation is obvious, as the long 
tunnel becomes a sluiceway, and through the whole length 
of which sluice-boxes are laid, for the double motive of 
carrying off the material and saving the gold, and for this 
purpose a trough of strong planks is placed in the tunnel, 
feet wide, and with sides high enough to contain the 
stream. The pavement of the trough is generally laid of 
blocks of wood 6 inches in thickness, cut across the grain, 
and placed on their ends, to the width of the sluiceway. 
The wooden blocks are usually alternated with sections of 
stone pavement, the stones being set endwise, and in the 
interstices between the stones and wooden blocks quicksilver 
is distributed, and as much as 2 tons of this metal is required 
to charge a long sluice. The water in the canal is brought 
by aqueducts, or other means, to the head of the mining 
ground, having an elevation of 100 to 200 ft. above the lowest 
level of the mining ground, and is finallyconveyed to it by iron 
pipes, sometimes sustained on a strong incline of timber. 
These pipes are of sheet iron, of adequate strength, 
rivetted at the joints, and measure from 12 to 20 inches in 
diameter, and communicate at the bottom with a strong 
prismatic box of cast-iron, on the top and sides of which 
are openings for the adaptation of flexible tubes, made of 
very strong fabric of canvass, strengthened by cording, and 
terminating in nozzles of metal of 2^ to 3 inches in dia- 
pieter. From these nozzles the streams of water are 
