e reduced by a small grade. The greater the amount of
dirt to be washed, other things being equal, the steeper should be the
grade; for a swift current will wash more dirt than a slow one. In many
claims the pay-dirt is full of large stones and boulders, weighing from
one hundred to five hundred pounds each, all of which must be carried
away through the sluice. Some are sent down whole, and others are
broken into pieces with sledge hammers before they are thrown into the
box. These require a swift current and a large body of water. The
larger the supply of water, the steeper the sluice is made, other
things being equal. Of course economy and convenience of working
require that the sluice should be near the level of the ground, and as
that may be steep or level below the claim, the grade of the sluice
must to some extent conform to it. There are thus a multitude of points
to be taken into consideration in fixing the grade of a sluice; but a
fall of less than eight or more than twenty inches, in a box of twelve
feet, would be considered as unsuitable for the board-sluice. Sometimes
the upper part of the sluice is made steeper so as to dissolve the
dirt, and the lower part has a small grade to catch the gold. The
clayey matter of ordinary pay-dirt is fully dissolved in a sluice two
hundred feet long with a low grade, so the use of the boxes beyond that
length is merely to catch the gold. There are claims however in which
the clay is so extremely tough that it will roll in large balls more
than a quarter of a mile through a steep sluice with a large head of
water, and come out at the lower end scarcely diminished in size.

The gold is caught in the sluice-boxes by false bottoms of various
kinds. It would not do to leave the smooth boards, for the water would
sweep all the gold away, and the boards themselves would soon be worn
through. The most common false bottom is the longitudinal riffle-bar,
which is from two to four inches thick, from three to seven inches
wide, and six feet long. Two sets of these riffle-bars go into each
sluice-box, the box being twice as long as the bar. A set of
riffle-bars is as many as fill one half of a box. They are wedged in,
from an inch to two inches apart; the wedging being used, because the
bars can more readily be fastened in their places, and more easily
taken up, than if nails were used. Before the work of sluicing
commences, all the boxes are fitted with riffle-bars, and the bottom of