Ch. 13: Principal Diamond Mines of S. Africa

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	PRINCIPAL SOUTH AFRICAN MINES 305 rock. It has one great advantage over the De Beers mines, in that the rim rock is very firm, and therefore is not liable to fall as the shale formations of Griqua-land, about Kimberley, do. The contour of the surrounding surface also is favorable both to the drainage of the mine, and the storage of water by easily constructed dams. The Premier crystals have a peculiar laminated appearance. Many of them also have an oily luster, and are quite blue. There are also many false colors. Nevertheless some are of the finest quality and color. It is a mine which yields the extremes. The percentage of bort and large crystals of gem material is greater than from any other mine. The immense Cullinan was of exceptional purity. All the stones cut from it, ranging from five hundred carats down, are flawless. In the beginning, the Premier washings gave extraordinarily large results; nearly one and a half carats to the load. (16 cubic feet, equivalent approximately to a ton, now constitute a load.) The average of June, 1903, was 1.45; of July, 1.47; but from that time the yield steadily declined, the average to October 31 being 1.29. The highest average for any month in 1904 was .92; the lowest .62. The highest in 1905, .85; the lowest .26. The highest in 1906 was .35 and the lowest of average material .27. The yearly average since the opening of the mine and the value per carat is as follows:

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