n the
tunnel, 21/2 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 finally conveyed to it by iron pipes,
sometimes sustained on a strong incline of timber.

These pipes are of sheet iron, of adequate strength, riveted 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 canvas, strengthened by cording, and terminating in
nozzles of metal of 21/2 to 3 inches in diameter. From these nozzles the
streams of water are directed against the face of the gravel to be washed,
exercising incredible effectivity.

The volume of water employed varies of course with the work to be done;
but it is not uncommon to see four such streams acting simultaneously on
the same bank, each conveying from 100 to 600 inches of water per
hour--1,000 miner's inches being equal to 106,600 cubic feet of water per
hour, constantly exerting its force under a pressure of 90 to 200 pounds
to the square inch, varying with the height of the column.

Under the continuous action of this enormous force, aided by the softening
power of the water, large sections of the gravelly mass are dislodged, and
fall with great violence, the _debris_ speedily disintegrating and
disappearing under the resistless force of the water, and is hurried
forward in the sluices to the mouth of the shaft, down which it is
precipitated with the whole volume of turbid water. Bowlders of 100 to 200
lb. in weight are dislodged and shot forward by the impetuous stream,
accompanied by masses of the harder cement which meet in the fall, and by
the concussion from the great bowlders the crushing and pulverizing agency
required is found to disintegrate it. The heavy banks, of 80 feet an