The tailings are run into the huge vats, and the cyanide of potassium a deadly poison percolates through, and carries off the gold in solution. Photo by Barnett & Co., Johannesburg] [Illustration: SECTION OF A GOLD MINE. (Photo by Horace W. Nicholls, Johannesburg)] These beds lie in series, that particular one which contains most of the gold being called the Main Reef series, comprising the Main Reef proper and a number of subordinate reefs or bands. The thickness of the Main Reef is from 3 to 12 feet, that of the Main Reef Leader 3 feet on the average, and the South Reef thinner than the latter, but having a richer gold contents than either. These are the beds chiefly worked, the gold being disseminated throughout the matrix mainly in crystals, visible gold being only occasionally seen, but in fairly regular quantities, so that the results of working, whether in the richer or poorer reefs, are capable of being accurately forecasted. The knowledge of the nature and extent of the beds has only gradually been brought together, and is still incomplete in parts even for the 15 miles section of the Rand which has been longest under working, and discoveries are of almost daily occurrence extending the sum of information regarding their composition and incidence. In the section situated between the Langlaagte Estate Mine in the west and the New Comet in the east, one profitable mine after another follows almost without a break. The eastern and western extensions are, for the main part, still _terra incognita_; but the several mines scattered along their stretch have confirmed the identity and value of the formation, which is held by experts to warrant the belief in the existence of wealth even exceeding the Rand proper.