254 THE DIAMOND MINES OF SOUTH AFRICA
mallets
and clubs. Then it was sifted in rocking troughs, fitted with sieves
like the placer miners' cradles, and the concentrate of pebbles and
crystals and coarse rock grains was spread on tables, or sheets of iron
and wood laid on the ground, where it was scraped over bv hand, and the
gems picked out. In this rough process a third and perhaps a half of
the smaller crystals were left in the waste ground, and the losses from
theft were enormous.
In 1874 there was a change for the better in the introduction of water in concentrating. By building dams and sinking
