JULV, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



175 



The rock is an eclogite, consisting mainly of red garnets 

 ranging in size from a hemp seed to a pea, and green 

 (chromiferous) augite. This eclogite is now regarded 

 as an igneous rock, and one of those which have 

 crystallized at a considerable depth from the surface. 

 Diamonds, with other forms of crystallized carbon, 

 have been found (though rarely) in meteorites, not only 

 in those of native iron, as at the Canon Diablo, but in 

 one composed of this metal crystallized with olivine and 

 augite, which fell in 1885 at Nova Urei in Russia. Pro- 

 fessor Moissan has made small diamonds by fusing 

 carbon in iron, and cooling the mass so as to cause 

 great pressure at the interior — an experiment which 

 has been repeated by Sir W. Crookes. We must, 

 therefore, conclude that the South African diamonds 

 originated in deep-seated igneous rocks. They have, 



View of the Cullinan Diamond, showing one of tli 

 cleavage plane. Appi 



vage pianes. 

 natural size. 



mately 

 From a Photograph by Sir William Crookes, F.R.S 



as yet, been detected only in eclogites, but we may anti- 

 cipate their occurrence in other crystalline rocks with a 

 lower percentage of silica, and especially in peridotites. 

 These deep-seated masses must have been stripped of 

 their covering and laid bare before the Triassic period 

 began; fragments were detached and rolled into pebbles, 

 forming the conglomerate at the base of the Karoo 

 series, which was duly covered up by the sandstones 

 and shales towards the end of this period. Move- 

 ments of the earth's crust in Southern Africa caused 

 discharges of lava, in the form of flows and dykes. 

 Then great explosions drilled huge holes through all 

 these, and hurled the shales, quartzite, conglomerate, 

 and the shattered crystalline floor into the air. This 

 mixed stuff, minerals and rock, as it fell back, finally 

 filled the pipes, which, however, continued to be vents 

 for gas, steam, and, perhaps, hot water. 



Such is the story of the diamond. There are several 

 other pipes more or less productive, most of which are 



scattered on a narrow belt about 125 miles in length, 

 which runs, roughly, in a N.N.VV. to S.S.E. direction 

 from Newlands on the Hart river in West 

 Griqualand to Faure Smith in the Orange State, 

 parallel, as Dr. Molengraff has pointed out, with 

 the line of the Drakensberg Range. But the group, 

 including the l^remier Mine, now famous for the 

 discovery of the Cullinan diamond, must belong to 

 quite another zone of disturbance, for it is about seven 

 leagues east of Pretoria (north of Van der Merve 

 Station). Here the pipes are driven through quartzite 

 and an igneous rock called felsite, so the I-iaroo shale 

 cannot have helped to make these diamonds. 



We must pass over the story of the working of the 

 mines, for it is a long and complicated one, contenting 

 ourselves with stating that, according to De Launay, 



richer mines produce 

 on an average about 

 15 grains weight of 

 diamonds to five 

 cubic yards of rock, 

 and that, by 1896, 

 .South Africa had 

 produced more than 

 double the quantity 

 of Brazil and India 

 together. A decade 

 earlier its mines in a 

 single year yielded 

 nearly 3 , 160,000 

 carats of diamonds. 



These stones fre- 

 quently show a very 

 faint resin-yellow 

 tint, but many are 

 perfectly colourless 

 and free from any 

 flaw. The first ex- 

 ceptionally fine one, 

 the Star of South 

 Africa, weighing 83^ 

 carats, was found in 

 i86g. Three years 

 later diggings on the 

 Vaal River produced 

 the Stewart, 228f 

 carats. The De 

 Beers Mine came to 

 the front in 1880 

 with a diamond 

 weighing 428^ carats, which was beaten four years 

 afterwards by one (locality uncertain) weighing 

 457i carats.—" On June 30, 1893, the Jagers- 

 fontein Mine (the best in the Orange River State) 

 broke the world's record by disclosing a diamond 

 weighing 9715 carats. It was rather irregular in shape 

 — something Hke a longish potato — measuring about 

 3 inches by a little less than i| inches." But on 

 January 25 in the present year that was left far behind 

 by the Cullinan diamond, which was found about 18 

 feet below the surface at the Premier Mine, Transvaal, 

 and of which we give a photograph. It is a stone 

 of excellent water, weighing about 3,024! carats.* 

 Yet this monster is itself only a fragment, for four of 

 its bounding faces are cleavage planes, and experts 

 think that the stone, when perfect, may have been quite 

 twice as heavy. 



* A carat is 3J grains, Troy. 



It is resting on another 



