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THE DISTRIBUTION OF GOLD IN SLUICES.
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257
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a high percentage of the gross yield of the mines is found in the undercurrents.
Hydraulic
mining in the " cement claims " is carried on under great difficulties.
An exhibit of the workings of the sluices of a representative " cement
claim " (French Corral) is here given, and the contrast thus afforded
with the workings of sluices in the majority of cases is most striking
and of especial interest.
The
washings from the French Corral mine, after passing through the new
tunnel, are successively distributed over nine undercurrents before
they are finally discharged. The sizes and arrangements of these
undercurrents are given in the accompanying table.
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From
January 14 to October 3, 1877, there were 163,263 miner's inches of
water discharged over these undercurrents, and the corresponding yield
of the wash-
* Grade 15 inches in 14 feet.
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