The diamonds are found in beds of clay, of which there are two layers: a soft, yellow clay, lying on or near the surface, and a hard, blue clay, lying deeper. These clays, which are usually covered by a thin stratum of calcareous rock, are supposed to be the remains of mud pits due to volcanic action, such as the boiling springs of the Yellowstone. Imagine a great hollow, looking like a gigantic bowl, perhaps half a mile in diameter and one hundred feet deep, enclosed by a series of barbed-wire fences and filled by thousands of Kaffir workmen, looking, from a distance, like a gigantic swarm of ants—such was my first impression of the Premier Mine. The native labourers, who work in three shifts of eight hours each, after cleaving the “hard-blue” with their picks, load it onto trolley-cars, which are attached to a cable and hauled to the surface of the pit, where it is spread on mile-long fields and exposed for several months to rain, wind, and sun so as to effect decomposition. The softened lumps of earth, after being brought into still smaller fragments by the pickaxe, are then sent to the mills, where they are crushed, pulverised, washed, and finally sent to the “greaser” to get at the stones. Until very recently men had to be employed to sort the washed “concentrates” and pick out the diamonds. But they would miss some. And the men had to be guarded lest they steal the gems. And detectives had to be hired to watch the guards who watched the men. But one day a mine employee named Kirsten happened to notice that the diamonds, no matter how small or discoloured, always stuck to a greasy surface, just as iron filings stick to a magnet, while the dirt and other stones did not. That was the suggestion which led to the invention of the “Kirsten greaser,” a series of sloping boards, heavily coated with grease, which are gently agitated as the mud and slime containing the diamonds are slowly washed over them, and which never fail to collect the precious stones.