Parent-Rock of the Diamond in South Africa. 97 



iially banded or bordered with a darker tint ; crystalline 

 rocks have also been noticed, though these appear to be 

 far from common, such as granite, diorite, and varietes of 

 eclogite.^ As to the genesis of the diamond, more than 

 one opinion has been expressed. Professor Lewis re- 

 garded the matrix as a porphyritic form of peridotite, 

 once a lava, now serpentinised,^ in which the diamond had 

 been formed by the action of the molten rock on some 

 carbonaceous material (probably the Karoo shale). Others 

 regarded the matrix as a true breccia, comparing it with 

 the agglomerates in volcanic rocks. But among the 

 latter, some thought that the diamond had been produced 

 in situ by the action of steam or hot water in a subsequent 

 solfataric stage of the volcano, while others (including 

 myself) held that it had been formed, like the garnets, 

 pyroxenes, &c., in some deep-seated holocrystalline mass 

 which had been scattered by explosions.^ 



The specimens which I am about to describe were 

 obtained at the ]Srewdands Mines, West Griqualand ; 

 from 40 to 42 miles from Kimberley, almost due IST.W. 

 Here the workmen occasionally came across well-rounded 

 boulder-like masses of rather coarsely crystalline rock, 

 studded with garnets, which are sometimes about a foot in 

 diameter. Specimens of these were found or obtained by 

 Mr. G. Trubenbach, the London manager of the JSTewlands 

 Diamond Mine Company, during a visit to the mines in 

 1897. His interest had already been aroused by picking 

 up a specimen, presently to be noticed, in which some 

 small diamonds occurred, very closely associated with a 

 garnet ; so the boulders were brought back by him to 



1 A. W. Steliizer, " Sitzuiigsber. u Abhandl. der Tsis " (Dresden), 1893 (April), ji. 

 71, calls attention to the fact that these show signs at attrition and that they range i]i 

 size from a few cubic iiiiVlimetres upwards, being sometimes large boulders. Among 

 the materials (at Kimberley) he mentions both granite and eclogite. 



2 For the rock itself he pioposed the name "kiniberlite." 



3 In other words, tljatthe volcano (as occasionally has liappened) had ejected little 

 or no lava or scoria, disidiarging only steam and hot water, with shattered ro<'k. This 

 view is held by Max Bauer, in ■' Edelsteinkunde," p. 225, which however, I had not 

 seen when this paper was written. 



7 



