The floor of the sluice is laid with riffles made of strips of wood 2 in.
Long ditches with stone-paved sluices for washing this mineral-bearing material have long been used by the Indians, who also construct stone bars across the beds of the streams to make riffles and hold the deposited grains of gold.
These are paved with stone blocks or lined with mercury riffles, so that from the greatly reduced velocity of flow, due to the sudden increase of surface, the finer particles of gold may collect.
It then passes through screens and grizzlies to retain the coarse gravel, the finer material passing on to sluice boxes provided with riffles, supplied with mercury.
Into the " rocker " and the " tom " the miner shovelled dirt, rocking it as he poured in water, catching the gold on riffles set across the bottom of his box; thus imitating in a wooden box the work of nature in the rivers.
The upper end contains a perforated riddle plate which is placed directly over the riffle box, and under certain circumstances mercury may be placed behind the riffles.
These were known originally as Hungarian riffles.
riffles for fish to spawn.
And secondly there are the shallow riffles, which are easy to fish but rarely hold anything worth catching.
Even when the mornings are still frosty in early March, dace will be found massing in the deeper water before shallow gravel riffles.
Water is poured on the dirt, and the rocking motion imparted to the cradle causes the finer particles to pass through the perforated bottom on to a canvas screen, and thence to the base of the cradle, where the auriferous particles accumulate on transverse bars of wood, called " riffles."
These help to create pools and riffles for fish to spawn.
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