DIAMOND: OCCURRENCE IN SOUTH AFRICA 187 



Dry Diggings. 



The nature of these deposits was not at first known, and they were supposed to be 

 similar to the river deposit and to consist merely of superficial layers of alluvium. It was 

 soon recognised, however, that this was by no means the case, and th^t the deposits were 

 absolutely unique in character. The geographical position of these deposits has been 

 already described, they are situated on a high plateau, far removed from any water- 

 coui-ses and formed of rocks belonging to the Karoo formation. This formation, which has 

 a total thickness of about 10,000 feet, consists of sandstones and shales with numerous 

 intruded dykes and bosses of igneous rocks, variously referred to, according to the form of 

 the mass and the character of the rock itself, as trap, dolerite, melaphyre, basalt, diabase, &c. 

 The age of the sedimentary rocks is not exactly knov/n as yet, but in any case they are later 

 than the Carboniferous, the lower beds probably corresponding with the Permian, and the 

 upper beds with the Trias of Europe. In this upper and younger part occur the deposits 

 of diamonds in Griqualand West which we have now to consider. 



The account which follows deals mainly with the half-dozen mines having the richest 

 yield, and specially with the four best known Kimberley mines, others being passed over as 

 insignificant or not completely examined. The main features of all are identical, and as the 

 individual deposits differ only in unessential points, it is unnecessary to consider each one 

 singly in any great detail. 



The diamond-bearing material is contained in pipes or funnel-shaped depressions which 

 penetrate the Upper Karoo beds in a vertical direction to an unknown depth. The outline 

 of a cross-section of one of these depressions may be circular, elliptical, kidney-shaped, or 

 •more or less irregular. The rock which fills these pipes differs entirely from the surrounding 

 beds of the Karoo formation, the so-called "reef," and is sharply separated from them. 

 The occun-ence of diamonds is confined exclusively to the material filling the pipes ; nowhere 

 in the surrounding reef of sandstone and shale, or elsewhere in the Karoo beds, has a single 

 stone been found, although enormous quantities of these rocks have been removed in the 

 course of the mining operations. 



The upper extremities of the pipes are elevated above the surface to the height of a 

 few yards each, thus forming a small kopje ; in the case of the Wesselton mine, however, 

 there was a slight depression. The pipes vary in diameter from 20 to 750 yards, the usual 

 diameter being from 200 to 300 yards. In 1892 the diamond-bearing material had been 

 excavated in the Kimberley mine, which is the deepest of all, to a depth of 1261 feet, and, 

 as in the other mines, with no sign of exhaustion ; the rock is therefore continued to an 

 unknown depth. 



The cross-sections of different pipes taken at the earth's surface differ widely both in 

 shape and area, as will be seen from the following data: Du Toifs Pan (Dutoitspan), 

 192,000 square yards' in area, of a flat horse-shoe shape, 750 yards long and 200 yards broad ; 

 Bultfontein, 118,000 square yards in area, almost circular in outline with a diameter of 

 363 yards ; De Beer's (De Beers), 66,000 square yards in area, elliptical in shape, measuring 

 320 yards from east to west and 210 from north to south ; Kimberley, 49,000 square yards 

 in area, oval in shape, 290 yards long and 220 yards broad, with a small projection 

 measurino- 37 yards towards the east. The size of the pipe of the Jagersfontein mine is not 

 exactly known, its cross-section is between 100,000 and 110,000 square yards ; exact details 

 respecting the Koffyfontein mine are also wanting, but in any case it is smaller than the 

 mine last mentioned. A peculiar feature of the Kimberley mine is the gradual contraction 



