1899] THE SOUTH AFRICAN DIAMOND 175 



any other known species. Three varieties of Kimberlite may be 

 distinguished: (1) Kimberlite proper, a typical porphyritic lava; 

 Kimberlite breccia, the same lava broken and crushed by volcanic 

 movements and crowded with included fragments of shale ; (3) Kimber- 

 lite tuff, being the fragmental and tufaceous portion of the same 

 volcanic rock. These varieties pass by insensible gradations one into 

 another, so that no sharp line can be drawn between them, and all 

 occur together in the same neck or crater." l He held that the 

 diamond was produced in situ, the basic magma of the peridotite 

 offering so little facility for the oxidation of the carbon. 



In this diversity of opinion two points had to be settled before the 

 genesis of the diamond could be determined : (a) whether that 

 mineral was authigenous — crystallised on the spot — in the so-called 

 Kimberlite ; and (b) what was the true nature of that rock. If it 

 were a serpentine, there was then a high probability (though not 

 certainty) that the diamond was authigenous and the date of its birth 

 later than the Triassic period ; if, however, the rock were a breccia 

 (produced by some form of volcanic explosion), it was then more 

 probable that the diamond, like many of the other minerals, had been 

 obtained from the shattering of some more ancient crystalline rock. 



My connection with this interesting and amicable controversy 

 began in 189 1, 2 when, at the request of Professor Eupert Jones, I ex- 

 amined with Miss C. A. Eaisin some minerals and small rock fragments 

 which he had received from South Africa. Of the former specimens 

 nothing more need be said since they were those usual in "washings"; 

 but the latter were clearly pieces of a coarse eclogite, consisting mainly 

 of a red garnet and a green augite (that now identified as chrome- 

 diopside) ; both being minerals found in the Kimberlite. This 

 investigation caused me to pay closer attention to the question, and the 

 circumstances mentioned in the Preface to the " Genesis and Matrix of 

 the Diamond," by my lamented friend Professor Carvill Lewis, led to 

 my undertaking (with the kind aid of Professor Ptosenbusch) to see 

 his manuscripts on this subject through the press. But before these 

 reached me I had the opportunity of examining two remarkably well- 

 preserved blocks of the breccia, brought from Kimberley by Sir J. B. 

 Stone, M.P. He kindly presented one of these to me, and a descrip- 

 tion of it and some other specimens is published in the Geological 

 Magazine. 3 I came to the conclusion, as there expressed, that the 



1 "Genesis and Matrix of the Diamond," p. 50. I may add that neither in Professor 

 Lewis's microscopic slices which I studied, nor in the rather numerous collection which I 

 possess, some of them unusually well preserved, have I been able to recognise these 

 three varieties. I have been for some years convinced that the rock was a breccia, and my 

 latest studies (Gcol. Mag., 1897, p. 448) proved to me that certain fragments which I had 

 thought might possibly represent a compact peridotite after serpentinisation, must have 

 had quite another origin. 



2 Gcol. Mag., 1891, p. 412. 



3 By myself and Miss Raisin, with a prefatory note by Sir J. B. Stone, Ckol. Mag., 

 1895, p. 496. 



