(or
1 inch per foot). A sheet-iron plate, perforated with holes half an
inch in diameter, forms the bottom of the lower end of the trough,
which is bevelled on the lower side, so as to have the plate on a level.
The
material, when fed in from sluices, on striking the riddle (or
perforated plate) is at once sorted, the fine dirt with the water
passing through it, while the coarser stuff is shovelled off.
Under
the perforated plate there is a flat box set on an incline, into which
the finer gravel passes. By the continual discharge of the water
through the plate, and with the occasional aid of the shovel, the sand
is kept loose, allowing the gold to settle. Since the introduction of
sluices the torn has disappeared.
