line
of drainage is once fixed and proves to be too high, it is a source of
endless expense, frequently fatal to the enterprise. Many instances
could be cited where, for want of properly conducted preliminary
investigations, tunnels have been driven on too high a level and
thereby the enterprises have resulted in failures.
At
the Pioneer Mine, Grass Flat, Plumas County, the original owners in
opening their claim ran a tunnel 4,000 ieet long. When midway in the
channel the tunnel was found to be 22 feet above the bed-rock. The sum
of $60,-000 expended in this work was a total loss, and the subsequent
purchasers were obliged to expend over $100,000 in properly opening the
mine.
SLUICES.
The
name "sluice" was originally applied by the miner to the sluice box.
Subsequently several sluice boxes were joined together for permanent
washing, and the word "flume" was used synonymously. The word sluice used
in the text refers only to troughs, cuts, or boxes in which or through
which gravel or dirt is washed, in contradistinction to the term flume, which is applied solely to wooden structures used for water conduits.
To
secure the maximum discharge sluices should be set on straight lines so
far as possible, and where curves occur the outer side of the box
should be slightly raised, in order to cause a more general
distribution of the materials over the riffles. When lines of sluices
have frequent curves it is customary to make no changes in the grades,
although to secure the greatest flow of material doubtless provision
should be made to overcome retardation by increased grades at and
below the curves. Sluices with drops are highly desirable for saving
gold.
Grade.—The facility with which gravel can be moved depends mainly on the inclination which is given to the
