Prof. Bonney and Miss Raisin — Rochs from Kimherley. 501 



(2) That it contains various rock fragments, some of them, 

 in all probability, having been formerly peridotites.^ 



(3) That it contains a considerable number of minerals of fair 

 size in a more or less fragmental condition {e.g., olivine, augite, 

 biotite, garnet, magnetite, ilmenite). 



(4) That these minerals — or at any rate most of them — are not 

 such as are likely to have been formed in situ, but more probably 

 have been obtained by the destruction of rather coarse peridotites, 

 pyroxenites, and eclogites.^ 



(5) That while, since the formation of the breccia, changes to 

 a not inconsiderable extent have taken place in the production of 

 serpentine, chlorite, perofskite, etc., these are not such as are 

 suggestive of a very high temperature or of very great pressure. 



We are therefore led to the following conclusions : — That the 

 diamond also was not produced in situ in the rock which we have 

 been describing, but, like the garnet, etc., had its origin elsewhere, 

 probably at a distinctly greater depth from the surface.^ We thus 

 agree with Professor Daubree,* and differ from the views expressed 

 by Mr. Hudleston^ and Prof. Carvill Lewis, ^ both of whom regarded 

 the diamond as produced in situ,'' but we agree with the former that 

 the " pipes " are probably of volcanic origin,^ and that heated water 



1 In the specimens which we have examined it happens that fragments of shale, 

 which according to Profs. Daubree and Carvill Lewis are sometimes abundant, are 

 either extremely small and rare or entirely absent. At any rate, they cannot now be 

 identified with any certainty. [Professor A. H. Green, F.R.S., since these words 

 were written, has most kindly lent me a number of specimens of rocks and minerals 

 which he collected when visiting Kimberley in 1882, together with sundry notes and 

 sections, of great interest. His specimens of "blue ground" are not quite so hard 

 as those described above, but are in better preservation than most that I have 

 examined. They contain fragments of black shale, in one case abundantly. One 

 specimen also includes several angidar fragments (up to a good half-inch in diameter) 

 of a compact, slightly streaky, greenish -yellow rock, apparently a rotten serpentine 

 (microscopic examination seems hopeless) . There are specimens also of other rocks 

 which occur as fragments in the breccia : three of these must have been of large 

 size ; two are amygdaloidal, one a compact diabase, the other a reddish porphyrite ; 

 the third an olivine basalt with some flakes of brown mica. Of smaller specimens 

 (not more than about an inch in diameter) six are from the Bloemf ontein Mine : one 

 is a diorite, very slightly foliated ; the other five are particxdarly interesting, tor 

 they represent a fairly coarse rock, chiefly composed of sahlite and a brownish mica, 

 indistinguishable from that described above in the breccia. There are also specimens 

 of the sheets of doleritic or diabasic rocks of the district. Dykes, sheets,^ etc., of 

 these, according to Professor Green, are very abundant, as described in his paper 

 (Q.J.G.S., xliv, pp. 254, 264). His sections make the "neck"-like character of 

 the diamantiferous rock very clear — T. G. B.] 



2 As described in our paper, Geol. Mag. 1891, p. 412. 



3 We may say that this conclusion was arrived at independently of previous 

 writers, for we did not refresh our memory of the opinions expressed by them till our 

 work was practically concluded. 



* Comptes Rendus, 1890, vol. ex, p. 18. 



^ Proc. Geol. Assoc, viii, p. 65. 



6 Brit. Assoc. Reports, 1886, p. 667; 1887, p. 720; and Geol. Mag. 1877, 

 pp. 22-24. 



' Prof. Maskelyne inclines to the opinion that the diamond was produced at or 

 near the contact of a basic igneous rock with a carbonaceous shale, but that since then 

 the whole mass has been affected by mechanical disturbances and thermal waters. — • 

 Q.J.G.S., vol. XXX, 1874, pp. 407, 408. 



8 This was Mr. Dunn's opinion, who supposed that the diamond was produced by 



