fle-bars
must be used; for with longitudinal riffle-bars or stones, there would
be too much danger of choking. These tunnel-sluices, because of their
low grades, require much more attention than any other kind of sluices.

_Ground Sluice._--All the sluices hitherto mentioned and described have
wooden boxes, but the ground-sluice has no box: the water runs on the
ground. The place selected for the ground-sluice is some spot where
there is a considerable supply of water, a steep descent for it, and
much poor dirt. The stream is turned through a little ditch, which the
miners labor to deepen and enlarge, and when it is deep they prize off
the high banks so that the dirt may fall down into the ditch. This is a
very cheap and expeditious way of washing, but it is not applied
extensively. It is used to the most advantage for washing where the
water is abundant for only a few weeks after heavy rains, and where it
would not pay to erect large sluices. A few cobble-stones should be
left or thrown at intervals in the bed of the ground-sluice to arrest
the gold, for if the bed were smooth clay, the precious metal might all
be carried off. Quicksilver is not used in the ground-sluice. After the
dirt has all been put through the ground-sluice, it is cleaned up in a
short board-sluice, or a tom.

_Long Tom._--The tom or long tom, an instrument extensively used in the
Californian mines in 1851 and 1852, but now rarely seen, is a wooden
trough about twelve feet long, eighteen inches wide at the upper end,
and widening at the lower to thirty inches, with sides eight inches
high. It is used like a board-sluice, but has no riffle-bars, and at
the lower end its bottom is of sheet-iron, perforated with holes half
an inch in diameter. This sheet-iron is turned up at the lower end, so
that the water never runs over there, but always drops down through the
perforated sheet-iron or riddle, into a little riffle-box, containing
transverse riffle-bars. A stream of water of about ten inches makes a
"tom-head"--or the amount considered necessary for a tom--through the
tom, which has a grade similar to that of a board-sluice. The dirt is
thrown in at the head of the tom, and a man is constantly employed in
moving the dirt with a shovel, throwing back such pieces of clay as are
not dissolved, to the head of the tom, and throwing out stones. From
two to four men can work with a tom; but the amount of dirt that can be
washed is not half that of a sluic