discharge
of 2,225 cubic feet of water in twenty-four hours. This main ditch
ramifieslihronghout the country for a total distance of over 40 miles,
and it delivers its contents into two mains, or distributing pipes,
constructed of sheef wrought iron, three-tenths of an inch thick only,
of a diameter of 30 inches each, gradually decreasing, however, at the
mines to half their size, in order to attain a greater pressure. These
pipes deserve particular attention,, on account of their great
strength, durability, economy, and portability; they are made of the
best Russian charcoal wrought-iron plates, riveted together
longitudinally, zig-zag fashion, with a good overlap, and the same
laterally. Generally four lengths are " telescoped" together, there
being no flanges or faucet joints, making each length a little over 17
feet, weighing about 260 lbs. each length; they are joined together
with the help of a screw-jack, and simply laid in a shallow furrow on
the surface. Expansion joints are provided by allowing an 8-inch
overlap here and there, instead of the ordinary 3 inches; and these
pipes are, undoubtedly, under certain conditions, superior to the
costly, cumbersome, and short-lengthed cast-iron pipes commonly used in
Victoria and elsewhere. They appear to last equally as well also,
inasmuch as pipes were inspected that had borne an enormous pressure
(when their very inconsiderable thickness of metal is considered)
during eight to ten years, and they had still their original tar and
asphaltum coating on, as when first laid down. This company washed
during 22-1/2 months 4,777,700 cubic yards of gravel with about 3,000
miners' inches of water per day, representing 80 tons of water each
day, and their yield of gold averaged about 24-1/2 cents of gold for
each miners' inch, or, as stated before, 5-1/2 cents for each yard of
gravel. These pipes are divided into " branches," each of which
supplies a " nozzle," from which a jet of water issues, which is the
principal motor of the gravels operated upon. There are 4-inch to
9-inch nozzles in use, and bymeans of knuckle, universal joints, and
balance-weights, these nozzles maybe directed anywhere, without the
least labor or difficulty. " Starting in" to "hydraulic" any ancient
river like that of this company (North Bloomfield) requires a careful
survey, and then a tunnel through the " rim " country from an adjacent
and deeper gulch; in this case such a tunnel was driven (and as ample
water pressure was available, a mining diamond drill was
utilized both for prospecting and blasting) for a distance of 8,000
feet, at a cost of 500,000 dollars, or £100,000. This tunnel measures 6
feet by.8 feet in the clear, and with a fall of 5 per cent, reaches the
main shaft in the gutter at a depth of 54 feet below the
gravel. This shaft is exceptionally well secured with very massive
timber, in order to withstand the immense strain put upon it by the
gravels and large boulders of rock, propelled by the jets from their
positions and hurled down the shaft into the tunnel, the bottom of
which is lined for 1,800 feet in length with quicksilver wells, set in
with a massive " wood pavement," which affords every means for the
collection of most of the gold.
In
order, however, to dislodge the tenacious " blue" gravel, it has been
found requisite to employ explosives to shatter it, and also to break
up the immense boulders found invariably in these gravels; and after
that the washing down of the enriched gravels, out of the pockets in
the bed-rock, proceeds systematically and effectively, without
hindrance. It will be observed that, in these cases the tunnels serve
not only as an outlet for the debris, but also as a means for
intercepting the gold liberated by the action of the water. With such
enormous quantities of poor gravel, it would not pay of course to use
much manual labor, and therefore the concentration, if one might say
so, of the gravel still containing gold is performed outside
