448 Professor T. G. Bonney — Roclcafrom Kimherley. 



III. — On some Eock-Specimens from Kimberley, South Africa. 

 By Prof. T. G. Bonney, D.Sc, LL.D., F.E.S., V.P.G.S. 



A PAPER on the diaraantiferous rock of Kimberley by Sir J, B. 

 Stone, M.P., Miss Raisin, and myself, was published in this 

 Magazine in 1895.^ Since then the first-named has received from, 

 friends in South Africa another parcel of specimens, obtained, at 

 a greater depth than heretofore, in the De Beers mine. These 

 specimens, twenty in number, he kindly entrusted to me for 

 description. They represent, as will be seen, not onl}?^ the 

 diamantiferons breccia, but also the associated igneous and sedi- 

 mentary rocks. Two specimens among the first-named appeared 

 to be in very good preservation : the others were more or less 

 decomposed, though much more solid than the material which was 

 brought to England in the earlier days of the industry. About the 

 same time I had the opportunity of examining a fine collection of 

 the minerals and rocks which had been obtained by Sir W. 

 Crookes, F.R.S.,^ during a recent visit to Kimberley. One specimen 

 of diamantif'erous breccia among these appeared to me in better 

 preservation than even that which formed the principal subject 

 of our former paper, so he kindly permitted me to have a piece 

 removed for microscopic examination, and a description of it is 

 included in this paper. During the present year the investigations 

 of the Kimberley rock left in manuscript by the late Professor 

 Carvill Lewis have been published,^ which give a much more 

 elaborate account of its mineral constituents than has hitherto 

 appeared. This enables me to pass rapidly over the mineralogical 

 part of the subject, and to restrict myself to a few details which 

 seem to me of some little petx-ological interest. The method of 

 working the mines, by sinking vertical shafts outside the area 

 of the "pipe" and driving from them horizontal levels at intei'vals, 

 is now so well known as to render needless any explanation of 

 the terms employed. I group the specimens, for purposes of 

 description, under three heads : (1) the diamantiferons breccia, 

 (2) the dykes and other igneous rocks, (3) the associated sedi- 

 mentary rocks. 



1. The Diamantiferons Breccia. 



Of this there are seven specimens, but slices have been cut from 

 three only, for the others, as was proved by a single trial, were not 

 sufficiently well preserved to give useful results. These three 

 proved to be in excellent condition. 



Four specimens come from the 1,200-feet level. They are rather 

 irregular in shape, and their volumes probably lie between 15 and 

 20 cubic inches.* They are numbered and labelled as follows : 



1 Geological Magazine, 1895, pp. 492, 496. 



^ Eeference to these is made in " The Genesis and Matrix of the Diamond," by the 

 late Professor H. Carvill Lewis, p. 69. 



^ " Papers and Notes on the Genesis and Matrix of the Diamond," 1897 

 (Longmans). 



* I mention the size here and elsewhere in order to show that my conclusion as to 

 the origin of the rock is not founded on small specimens, which in the case of so 

 variable a rock as the breccia is of some importance. 



