1897.] on Diamonds. 479 



from Kimberley : taking the yield of the Kimberley and De Beers 

 mines as worth, all round, large and small, 26s. &d. a carat, the drift 

 diamonds are worth 40s. 



The town of Kimberley is a remarkable instance of rapid growth 

 (Fig. 2). It has an excellent clnb and one of the best public 

 libraries in South Africa. Parts of the town, affectionately called 

 " the camp " by the older inhabitants, are still in the galvanised iron 

 or " tin shanty " stage (Fig. 3), and the general appearance is unlovely 

 and depressing. Reunert reckons that over a million trees have been 

 felled to supply timber for the mines, and the whole country within 

 a radius of 100 miles has been denuded of wood, with most injurious 

 effects to the climate. The extreme dryness of the air, and the 

 absence of trees to break the force of the wind and temper the heat 

 of the sun, probably account for the dust storms so frequent in 

 summer. The temperature in the day frequently rises to 100° in the 

 shade, but in so dry a climate this is not unpleasant, and I felt less 

 oppressed than I did in London the previous September. Moreover, 

 in Kimberley, owing to the high altitude, the nights are always 

 cool. 



The five noted diamond mines are all contained in a circle 

 3^ miles in diameter (Fig. 4). The mines are irregularly shaped 

 round or oval pipes, extending vertically downwards to an unknown 

 depth, retaining about the same diameter throughout. They are 

 said to be volcanic necks (Fig. 6), filled from below with a hetero- 

 geneous mixture of fragments of the surrounding rocks, and of 

 older rocks such as granite, mingled and cemented with a bluish 

 coloured hard clayey mass, in which famous blue the diamonds are 

 hidden. 



The breccia filling the pipes, usually called " blue ground," is a 

 collection of fragments of shale, eruptive rocks, boulders, and crystals 

 of many kinds of minerals. 



The Kimberley mine for the first 70 or 80 feet is filled with what 

 is called "yellow ground," and below that with "blue ground." 

 This superposed yellow on blue is common to all the mines. The 

 blue is the unaltered ground, and owes its colour chiefly to the 

 presence of lower oxides of iron. When atmospheric influences have 

 access to the iron it becomes peroxidised, and the ground assumes a 

 yellow colour. The thickness of yellow earth in the mines is there- 

 fore a measure of the depth of penetration of air and moisture. The 

 colour does not affect the yield of diamonds. 



The diamantiferous clay or blue ground shows no signs of passing 

 through great heat, as the fragments in the breccia are not fused at 

 the edges. The eruptive force was probably steam or water-gas, 

 acting under great pressure but at no high temperature. According 

 to Mr. Dunn, in the Kimberley mine, at a depth of 120 feet, several 

 small fresh-water shells were discovered in what appeared to be 

 undisturbed material. 



Let me cite a description of a visit to Kimberley in 1872, by 



