310 Professor T. G. Bonney — Parent-rock of the Diamond. 



These, occasionally, but not generally, are rather abundant. In 

 some cases they are chips of the neighbouring black shale, but in 

 others they are greyish-coloured with a somewhat porcelainised 

 aspect. The latter are generally subangular in form and externally 

 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 varieties of eclogite.^ As to the genesis of the 

 diamond, more than one opinion has been expressed. Professor 

 Lewis regarded tlie 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 solfatario 

 stage of the volcano, while others (including myself) held that it 

 had been formed, like the garnets, pyroxenes, etc., in some deep- 

 seated holocrystalline mass which had been shattered by explosions.^ 

 The specimens which I am about to describe were obtained at the 

 Newlands Mines, West Griqualand ; from 40 to 42 miles from 

 Kimberley, almost due N.W. Here the workmen occasionally came 

 across well-rounded boulder-like masses of rather coarsely crystal- 

 line 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 Newlands 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 brouglit back by 

 him to England. On careful examination a small diamond was 

 detected on the surface of one of these. On breaking the boulder 

 others were revealed. The most interesting fragment was sent by 

 Mr. Trubenbach to Sir W. Crookes, who showed it to me. Exami- 

 nation with a hand lens convinced me that the rock could not be 

 a concretion of the 'blue ground,' but was truly holocrystalline and 

 allied to the eclogites. Sir W. Crookes generously waived his own 

 claim to study the specimen, and obtained for me permission from 

 Mr. Trubenbach to have slices cut from it. I gladly take this 

 opportunity of expressing my gratitude to both gentlemen ; to 

 Sir W. Crookes for allowing me to carry out this interesting 

 investigation, and to Mr. Trubenbach for his great liberality in 

 placing at my disposal a considerable suite of specimens (including 



1 A. "W. Stelzner, " Sitzungsber. u. Abhandl. der Isis " (Dresden), 1893 (April), 

 p. 71, calls attention to the fact that these show signs of attrition and that they 

 range in size from a few cubic millimetres upwards, being sometimes large boulders. 

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



- For the rock itself he proposed the name ' kimberlite.' 



3 In other Avords, that the volcano (as occasionally has happened) had ejected 

 little or no lava or scoria, discharging only steam and hot water, with shattered 

 rock. This view is held by Max Bauer, in " Edelsteiukunde," p. 225, which, how- 

 ever, I had not seen when this paper was written. 



