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 
voleanic 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.”’ 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 (6) 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 1891,’ when, at the request of Professor Rupert Jones, I ex- 
amined with Miss C. A. Raisin 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 Rosenbusch) 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. 1 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 (Geol. Mag., 1897, p. 448) proved to me that certain fragments which | had 
thought might possibly represent a compact peridotite after serpentinisation, must have 
had quite another origin. 
* Geol. Mag., 1891, p. 412. 
* By myself and Miss Raisin, with a prefatory note by Sir J. B. Stone, Geol. Mag., 
1895, p. 496. 
