148 THE DIAMOND MINES OF SOUTH AFRICA
where
garnets and peridot were thickly deposited in the gravel, and this
observation was in accord with current accounts of mining in other
diamond fields. So the occurrence of these red and green pebbles was
commonly hailed as an assurance of the presence of diamonds, and gravel
so charged was washed and sorted with exceptional care. But there was
no concentrated deposit in this field like the cascalho in the
Brazilian river valleys, and the labor of washing the thick mass of
loose gravel was necessarily great.
There
were no appliances for handling and concentrating the gravel marking
any noticeable advance above the slow and laborious methods of the
Brazilian and Indian placer workers. The deposit was a mass of gravel
and sand, thickly sprinkled throughout with heavy boulders of basalt
and melaphyre which were laboriously pried and dragged out of the
shallow pits sunk by the miners.1 The mixed gravel and sand
was shovelled into wheelbarrows or carts and taken to the river's edge,
where it was dumped into heaps on the ground, or in troughs sunk in the
bank. Then the gravel was washed in cradles, with two or three screens
of perforated iron, or zinc, or wire mesh, set to form partitions with
discharge holes so graduated that the larger stones were held above the
upper and coarser screen, while the sand and lighter gravel flowed out
through the upper and lower screen holes. Meanwhile the cradle was more
or less expertlv shaken to cause a deposit of the gravel of high
specific gravity on the bottom between the screens. The worthless
stones in the upper part of the cradle were then picked and scooped out
by hand and thrown away, while the concentrate was taken out carefully
and carried to the sorting table, an ordinary deal stand or any level
wooden or iron structure, or to a flat stone. Here the deposit was
spread out thinly and sorted over inch by inch with a short scraper of
hoop iron, or any other thin strip, while the appearance of a diamond
was more or less keenly watched for.2
1 "The Diamond Diggings of South Africa," Charles Alfred Payton, London, 1872.
* Ibid.
