Professor T. G. Bonney — Parent-rock of the Diamond. 311 



other boulders) from the Nevvlauds Mines, and for the trouble which 

 he has taken in affording me the necessary information. 



Prior to the discovery just mentioned, one or two instances had 

 occurred at the De Beers Mine of a diamond apparently enclosed by 

 or projecting into a pyrope. One such, the garnet being the size of 

 a rather large pea, is in the collection at Freiberg (Saxony), to 

 which it was presented in 1892.' 



The specimen found by Mr. Trubenbach at the Newlands Mine 

 was a piece of blue ground, with a pyrope projecting from one 

 angle. A small, apparently broken, diamond seems embedded at 

 the top. The others (five) are well crystallized, two on one side, 

 three almost in contact on the other. The pyrope (which has 

 a kelyphite rim) seems to be indented by two, but to have once 

 included the others, as they are in contact with the unaltered 

 mineral. We were thus brought so far as to associate the diamond 

 with the pyrope ; though this proved no more than the presence of 

 garnets in the parent rock of the diamond, and thus made the 

 eclogite (already known to occur) highly probable, for, as observed 

 by Professor K. Beck,- the specimen itself is blue ground. In 

 confirmation of his statement I pulverized a fragment,^ and find 

 that the powder corresponds with the matrix of the blue ground 

 when similarly treated. The latest discoveries enable me to 

 complete the chain of evidence. 



Eclogite Boulders containing Diamonds. 



The first-named, tliat containing several diamonds, is a fragment 

 (perhaps from a quarter to a third) of a boulder, which probably was 

 ellipsoidal in shape, two of the axes being nearly equal and the 

 third distinctly the longest. We may infer that it was rounded 

 from a roughly rectangular block, since the curved surfaces are 

 slightly flatter in the middle parts. The axial lengths in the 

 fragment (prior to removing a piece from one end) were approxi- 

 mately 4 in. by 3 in. by 2 in. The rock is coarsely granular, 

 apparently composed of two green-coloured minerals, one darker 

 than the other (possibly only different states of a single mineral), 

 and of rich resin-pink coloured garnets, varying in size from a hemp 

 seed to a pea, with slightly irregular distribution. The outer 

 surface of the boulder, except for a very small ' step ' on one side, 

 is smooth, the garnets barely, if at all, projecting. The latter are 

 covered with a rather soft, dark skin, sometimes slightly thicker 

 than the thumb nail, which often has partly fallen off. This, as 

 can be seen on the broken surfaces, becomes less conspicuous in the 

 inner part of the boulder, and is sometimes invisible to the unaided 

 eye. Two small diamonds are exposed on the curved outer surface. 

 one about half, the other about one-fifth, of an inch from the edge 



1 A."W. Stelzner, " Sitzimgsber. der Tsis zu Dresden," 1893, s. 85, and R. Beck, 

 "Zeitsch. fiir praktische Geologie," 1898 (May), p. 163. 



^ Ut supra. 



•^ I could not advise Mr. Trubenbach to have a slice cut from the specimen, as 

 I feared it might be injured, but he kindly detached a little fragment from the 

 opposite end to that named above, which I have thus examined. 



