May 22, 1885.] 



♦ KNOWLEDGE ♦ 



439 



sheets which have been injected, as it were, between the 

 strata, am) as more or less vertical walls or dykes : in com- 

 position they closely resemble the ordinary " trap " or 

 basalt, such as forms the "Great Whin Sill" of Northum- 

 berland, and the Kowley Hills, near Dudley. It is needless 

 to say that the hot rock has affected the shales in its 

 immediate vicinity ; they are hardened, and the coal is 

 converted into stone-coal or anthracite. 



J 



n 



u 



r 



Fig. 1. — Showing the 400 " claims " into wliich the surface of the 

 Kimberley Diamond Hine was originally divided. 



But the diamonds do not occur in either the ti-ap-rocks 

 or the shales ; they are confined to certain vertical pipes or 

 " necks," which are believed to be the channels of commu- 

 nication by which melted matter rose from below to 

 volcanic craters now swept away. We will describe 

 the Kimberley mine as a type of the rest. All over the 

 sarface of the level plains of Griqualand red sand is spread 

 to a depth of from two or three inches to as many feet ; 

 below this comes atufaceous limestone (a deposit extracted 

 by the influences of the weather from the rocks below) of 

 simUar thickness, and below the limestone we find either 

 shale or trap-rock, or, if we are lucky enough to hit 



Pig. 2. — ^Vertical section of the Kimberley Diamond Mine, 

 showing the different rocks passed through. The dotted line A A' 

 marks the present level of the workings. 



upon it, the diamantiferous rock itself. At Kimberley, 

 formerly known first as " New Rush " and then as Coles- 

 berg Kopje, the old crater-neck occupies an oval area of 

 about twelve acres, which has been excavated to a depth of 

 450 ft. The walls, or sides, of this enormous hole are 

 composed partly of shale — bent upwards near its contact 

 with the diamond rock — and partly of trap. As the mine 

 deepens, the sides frequently fall in, and great trouble has 

 recently been experienced from this cause. The material 

 filling the pipe, and containing the diamonds, is of an 

 extraordinary and heterogeneous nature. The matrix is a 

 greenish mineral called bronzite (a bydrated silicate of 

 magnesia), but it includes thousands of rock-fragments. 



Tlie shales, the trap-rocks, other rocks such as gneiss, 

 which do not croj) out at the surface in this region, all 

 these occur in the pipe in masses of every conceivable size, 

 form, and shape. The whole points irresistibly to the 

 conclusion that the bronzite was forced up from biilow in 

 a melted state, and that it has broken through, incorpo- 

 rated, and carried upwards fragments of all the rocks 

 through which it has passed. 



The diamonds are found embedded in the greenish 

 matrix. They are crystallised in the octahedral form, or 

 in one of its derivatives. They are frequently found 

 broken or fragmentary, or even as mere splinter.s (for the 

 diamond is a rather brittle stone), but the missing frag- 

 ments of any one stone are nevev found, although they 

 have been diligently looked for. 



Kimberley Mine, with its neighbours, was annexed by 

 the British Government, in the interests of order, in 1871. 

 It is divided into 100 claims, each 10 yards square, on each 

 of which a Government royalty of lOs. per month has to 

 be paid. As the stuff is excavated, it is drawn up l)y 

 steam-power, along wire ropes, to the surface. Here it is 

 washed and sifted by machinery, the residue being lastly 

 passed over the sorting-tables, where the diamonds are 

 picked out. Owing to the large scale on which the opera- 

 tions have now to be conducted, most of the claims are 

 united into companies. The following extracts from 

 the balance-sheet of the " Central Diamond mining Com- 

 pany," Kimberley, for the year ending May, 1883, will 

 give some idea of the scale of work and the profits. 



Quantity of diamond-rock that has been hauled up = .3 14,205 loads, 

 16 cubic feet each. 



Quantity of diamonds found = 471,488 carats. 

 Quantity of diamonds sold = 434,890 carats. 

 Value of diamonds sold = £'.tS2,31-t. 

 Value of plant at the mine = £98,871. 

 Expenses of working = £253,920. 

 raid for rates and licences = £147,709. 

 Amount paid as dividend = £100,951. 



It will be seen that the rough diamonds were sold at the rate 

 of about one guinea per carat, but this would include much 

 " bort," as the diamonds which are useless for ornamental 

 purposes are called. A cut brilliant of good quality, 

 weighing one carat, is sold by jewellers at from £8 to £10, 

 and above this weight the value increases as the sqvMre of 

 the weight in carats. Thus a diamond of the "first" 

 water, weighing ten carats, is theoretically valued at 

 10xlOx£10=£l,000. The largest diamond hitherto 

 found in South Africa is the " Stewart," which weighs 

 288 carats (about 2 ounces troy) ; but the " Star of South 

 Africa," 83i carats, and the " Porter- Rhodes " are also 

 very fine gems. Many of the stones have a pale yellow 

 tinge, but others are quite equal to the best specimens ever 

 obtained from India or Brazil. 



{To he continited.) 



Amongst the most recent applications of the .^ilolus Water-spray 

 System of Ventilation are those at the New Registry-room, G.P.O. ; 

 St. John's Church, tt'aterloo-bridge-road, S.E. ; Dr. Voysey's 

 Church, Swallow-street, Piccadilly ; " Greenlands," the seat of 

 Eight Hon. W. H. Smith, M.P., Henley-on-Thames; St. John's 

 Church, Gainsborough ; Buckfastleigh Abbey, Devonshire ; St. 

 Mary's College, Wolverhampton ; Hospital, Singapore ; New Daily 

 Press Offices, Bristol ; Dr. Sharp's, Cnrzon-street, Mayfair, W. ; 

 Highfield Chapel, Earlsheaton ; New Butcher's H.all, Bartholomew- 

 close ; Christ Church (Congregational), Rhyl; Portland Prison; 

 Parkhurst Prison ; Hindlip Church, Worcester ; West Ham Police- 

 court; Chapel of St. Bartholomew; Convalescent Home, Swanley; 

 and Oldham-street shops, Manchester (third order). 



