DIAMONDS	17
	from the mines the blueground is conveyed to the floors — large flat areas — where it i sleft from three to six months, or more, to soften. These floors are very large, those of the DeBeers and Kimberley mines covering two thousand acres. The blueground on the floors is har­rowed by steam traction engines to assist in pulverizing the ground. This, with the action of the sun and rain, finally disintegrates the material so that it can be taken to the washing machines or pulsators, as they are technically called. The yield of diamonds per load of blue-ground is very small, but by the careful and comprehensive methods used, practically no dia­monds are lost and the total yield is very large. Of the South African mines the Kimberley and DeBeers have until recently produced most of the diamonds. These mines have now been worked so deep, about three thousand feet, that, owing to the heat and danger at that depth, they are at present considered about worked out and comparatively, few stones now come from these mines. The Dutoitspan mines are at present the largest producing mines in South Africa, and give very sound material, about the same as that of the Kimberley, DeBeers, and Wes-selton. The Bulfontein in point of production is the second largest mine under the DeBeers