OCTOBEK 1, 1801.] 



KNOWLEDGE 



1S7 



forced up from below, the sandstone and so forth 

 which show evidence of aqueous action being undoubtedly 

 derived from the material of the formerly existing rock. 

 This point has an important practical bearing, as an 

 aqueous deposit must be bottomed sooner or later, which 

 is scarcely likely to occur in the case of an eruptive forma- 

 tion ; hence the probability that the supply of diamonds 

 will continue to hold out. The extraction of the diamonds 

 from the blue is less readily effected than from the yellow 

 surface material. The blue rock is first spread out on the 

 surface and exposed to the action of the weather. The 

 disintegration proceeds best when wet and fine days 

 alternate, and in dry weather the process is hastened by 

 watering the material. The change which occurs is the 

 same as that which produced the yellow at the surface 

 of the pipes. When the process has gone on sufficiently 

 long, the rock is treated by the washing machinery. The 

 lighter materials are washed away in a pulsator, and the 

 diamonds and heavier minerals, such as pyrites and garnet, 

 are left in a sort of mud, which is brought on to a table and 

 carefully searched. Comparatively few diamonds are dis- 

 covered during the actual mining of the rock ; they are 

 imbedded singly, and are not conspicuous objects. The 

 general appearance of the natural diamond is somewhat 

 like that of a piece of white gum— the brilliancy of the 

 stone being only called out by the operation of cutting. 

 Naturally the stones most likely to be noticed are those of 

 large size, and it is these which are the great prizes of 

 diamond mining, since the value of a stone rises in a very 

 rapid ratio with the size. 



Now that the mining is no longer done by private 

 adventurers, but the whole worked under one manage- 

 ment, it is extremely important to ensure that the workers 

 shall not secrete the stones. The miners, when they 

 come up at the end of their shift, are carefully searched. 

 As the natives work without clothes it might be supposed 

 that the searching would be a very simple matter ; it is 

 not so, however, the hair, ears, and teeth being used as 

 places of concealment. The stones were frequently swal- 

 lowed, which led to the system of keeping the native 

 workers in compounds, which they are not allowed to leave 

 during the term of their engagement. No spirits are 

 allowed in the compounds, where the "boys" are well 

 taken care of. The life, with its order, and enforced dis- 

 cipline, often exercises a beneficial ei!'ect on the characters 

 of the natives, making them sober and saving. The laws 

 against receivers of stolen diamonds are very severe, 

 I.D.li.'s (illicit diamond buyers) being sentenced to six or 

 even ten years' hard labour. Most of the work at the larger 

 mines is done by contract, the company paying so much a 

 load, and providing and housing the native labourers, who 

 are paid by the person undertaking the contract — gene- 

 rally himself an experienced minor. There are about 

 seven natives to one white man in the mines : of the 

 whites some GO per cent, are Uritish, about -1 per cent, 

 other Europeans, or Americans. 



Now that the mining is carried on at great depths, the 

 risks of accident are considerable. Till a depth of about 

 •100 feet was reached the system of open workings was 

 followed, but as the depth increased the falls of the blue 

 rock became more frequent. Zulu watchers were stationed 

 to give warning to the miners when the rock showed signs 

 of giving way. This kind of work involving constant 

 alertness during long periods of inaction is peculiarly 

 trying to white men, but is admirably performed by the 

 Zulus. 



The appearance of the mines from above is that of huge 

 craters, at the bottom of which the tunnelling and shaft- 

 sinking commences. A depth of some 800 feet has been 



reached in some of the mines. The mode of descent into 

 these huge craters is simple and expeditious, but not suited 

 to nervous passengers. A kind of truck or tub is suspended 

 below two wire ropes, the flanged wheels, which are, of 

 course, above the tub, running on the ropes. The tub is 

 attached by a third wire rope to a winding engme, the rate 

 of windmg being about 40 feet a second, or nearly 30 miles 

 an hour. 



The average weight of diamonds obtained per load (16 

 cubic feet) of blue rock varies greatly in the different 

 mines ; the ordinary limits may be put at I- and 2^ carats. 

 Those mines which have the largest number of stones do 

 not generally produce the best quality, so that in the matter 

 of profit there is a sort of compensating arrangement. The 

 comparatively new .Jagersfontein mine sends stones of finer 

 quality than the better known Kimberley and De Beers 

 mines. During 1889 the total output of diamonds from 

 South Africa was four million carats, or about ^ of a ton, 

 the value of which may be estimated at rather more than 

 £1 per carat, or more than four million pounds sterling. 

 The finest diamonds at present m the market come from 

 South Aft-ica— notwithstanding the popular prejudice 

 which assigns all diamonds of " the first water " (a term, 

 by the way, which is not customary among diamond 

 merchants, though dear to lady novehsts) to the mines of 

 Golconda or Brazil. Diamonds, exceeding the Koh-i-noor 

 in size and equal in brilliancy, have been found in the 

 South African mines, but such stones are no longer sought 

 after. Their price, calculated to rise rather more rapidly 

 than the square of the weight, is nominally very great, 

 but no one will pay the price ; and, strange as it may seem, 

 such stones are now spht up into two or three of the 

 largest size that are ordinarily worn. The "crowned heads" 

 are apparently now all furnished with crowns, and dia- 

 monds of a size which seems only suitable for regalia can 

 no longer be disposed of. 



To the muieralogist the chief interest of the South 

 African mines lies in the fact that the blue rock, or " kim- 

 berlite,'' appears to be the original matrix of the diamond. 

 Till of late years the diamond had only been found in 

 alluvial deposits, its mode of occurrence giving no indica- 

 tion of its mode of formation. In kimberlite, however, it 

 appears in siti(, and the character of the minerals with 

 which it is associated may perhaps afford some guidance 

 as to the means to be adopted for the reproduction of 

 diamond. The rock belongs to the class termed ultra- 

 basic, having a low. percentage of silica and a high specific 

 gravity. The analogy of the rock to certain meteorites 

 has been referred to in a previous article. 



The following arc the principal minerals of the rock : — 

 Blotite ' Ihnenite 



Bronzite OUvine 



Chrome diallage Perowskite 



Chrome iron ore Pyrites 



Garnet Smaragilite 



Graphite 

 The olivine occurs in largo quantity. This mineral, 

 under the action of weathering, is decomposed, forming 

 serpentine. In studying the occurrence of diamond- 

 bearmg sand and deposits in different parts of the world, 

 the late Professor Carvel Lewis arrived at the conclusion 

 that diamond-bearing deposits occur, as a rule, in water- 

 courses which take their origin in mountainous tracts 

 characterized by the presence of serpentine. Serpentine, 

 or a rock which weatlicrs to serpentine, was considered 

 by Lewis to be the real matrix of the diamond. The 

 position and mineralogical character of the kimberlite 

 rock, filhng in the neck of a volcanic vent, plainly 

 show its igneous origin, and the fact that it has 



