poor
men who could scarcely afford to hold any stock of blue ground for the
sake of increased returns, even if they had been able to guard their
depositing floors from theft. After pounding the broken rock it was
sifted in the midst of dust clouds by rockers swung on riems of
rawhide, and the concentrate was then scraped over and sorted.1
In July, 1871, a large cylindrical revolving sieve, driven by a small
steam engine, was put at work by some American miners, and this sifting
machine was said to be an efficient and rapid separator. The pulverized
ground was thrown into the upper end of the screen, which was
1 "South African Diamond Fields," Morton, 1877. "Diamonds and Gold in South Africa," Reunert, 1893.
