Geology and Natural History. 77 



Then the volcano, after some more lava had struggled to reach 

 the surface (forming, at any rate, the dykes in the necks), passed 

 into a solfatara stage, during which the numerous secondary 

 changes mentioned above were produced, the carbonates were 

 deposited, and the minor structure of the mass was obscured. 

 Afterwards ordinary meteoric agencies began to work ; water 

 percolating from above still further affected the mass, more espe- 

 cially in its upper parts, producing the " yellow ground " and the 

 " soft blue " and depositing tufa. 



The result of this examination is to confirm me in my opinion 

 that the diamantiferous rock — the so-called Kimberlite — is a vol- 

 canic breccia rather than a peculiar form of peridotite. While it 

 is difficult, owing to secondary changes, to demonstrate the frag- 

 mental character of the matrix, I have failed to identify it with 

 any form of peridotite (or serpentine) known to me, and I cannot 

 understand how masses of that rock, the smallest of which is 

 about 370 yards in diameter, masses of which one has been traced 

 to a depth of 500 yards, could remain throughout in a practically 

 uniform glassy condition. 



6. Les Diamants du Cap; par L. De Laihstat. 226 pp., with 

 many illustrations. Paris, 1897 (Baudry et Cie.) — The subject 

 of the diamond production of South Africa is one which never 

 fails to be of interest, and this recent contribution to it by Pro- 

 fessor L. De Launay deserves the attention it will have Irom 

 many readers. The author is well-known from his earlier vol- 

 umes, the first an exhaustive treatise on mineral veins in general 

 (this Journal, vol. xlvi, 309, 1893), and the second on the gold 

 mines of the Transvaal (ibid., ii, 88, 1896). 



The present volume does not attempt to be a complete treat- 

 ment on the diamond — such an one, for example, as was pub- 

 lished some years ago by M. Boutan, — but is limited to the occur- 

 rence in South Africa with only a brief allusion to other regions. 

 A recent visit to Africa has given the author opportunity to make 

 original observations for himself. An account is given of the 

 early discoveries here in 1867, and the gradual development of 

 the industry from the time when a multitude of individual claims 

 were worked at the various localities to the present condition of 

 affairs, where the whole output is practically controlled by one 

 syndicate. It is interesting to note that according to the table 

 given by the author, the African mines in Griqualand have 

 yielded since 1867 about 12,000,000 kilograms of diamonds, 

 valued at $360,000,000 ; this does not include the production of 

 the Jagersfontein mine in the Orange Free State. A figure is 

 given of the largest diamond which has been found — the Excel- 

 sior diamond of Jagersfontein ; this is a mass of a rather irregu- 

 lar triangular form, three inches in its longest dimension and 

 weighed as found 971 carats. 



An interesting account is given of the geology of the deposits, 

 with numerous illustrations, and then the author goes on to dis- 

 cuss the method of exploitation and the treatment of the various 

 materials brought up in the mining. In regard to the method of 



