It was soon found that the diamonds of South Africa were not confined to the river gravels, and 'dry diggings' came to be established in the so-called 'pans.' The principal mines are those of Kimberley, De Beer's, Du Toit's Pan, and Bultfontein. The land here, previously worth only a few pence per acre, soon rose to a fabulous price. At these localities the diamonds occur in a serpentinous breccia, filling pipes or 'chimneys,' generally regarded as volcanic ducts, which rise from unknown depths and burst through the surrounding shales. The 'blue ground,' or volcanic breccia containing fragments of various rocks cemented by a serpentinous paste, becomes altered by meteoric agents as it approaches the surface, and is converted into 'yellow earth.' At Kimberley the neighbouring schists, or 'reefs,' are associated with sheets of a basaltic rock, which are pierced by the pipes. About 2000 white men are employed in the industry, and about 4000 blacks, who earn, on an average, about £3 a week. In the year 1887 the production of the principal mines was over £4,000,000. The production for 1894 was somewhat less, while the total value of diamonds exported from 1867 to 1894 was about £70,000,000.
The great number of large stones found in the mines of South Africa, as compared with those of India and Brazil, is a striking peculiarity. In the earliest days of African mining a diamond of about 83 carats was obtained from a Boer. This stone, when cut, yielded a splendid colourless brilliant of 46-1/2 carats, known as the 'Star of South Africa,' or as the 'Dudley,' since it afterwards became the property of the Countess of Dudley, at a cost of £25,000. Some of the African stones are 'off coloured'--that is, of pale yellow or brown tints; but a large gem of singular purity was found at Kimberley in 1880. This is the famous 'blue-white' diamond of 150 carats, known from the name of its possessor as the 'Porter Rhodes.' At the De Beer's Mine was found, in 1889, the famous stone which was shown at the Paris Exposition. It weighed 428-1/2 carats in the rough, and 228-1/2 carats when cut. It measured one inch and seven-eighths in greatest length, and was about an inch and a half square.