462 Transactions of the South African Philosophical Society. 



1897, pp. xvi. (Preface by Prof. T. G. Bonney, viii-xii), 72, 

 2 plates, and 35 text illustrations. [South African Public 

 Library, 635, E 84.] 



The book consists of two papers by the late Prof. Lewis — 

 the first, " On a Diamond-bearing Peridotite and on the History 

 of the Diamond " (read to the British Association at Birming- 

 ham in 1886), the second, " The Matrix of the Diamond " (read 

 at the British Association Meeting at Manchester in 1887), and 

 a third by Prof. Bonney on " Kimberlite from the United 

 States." 



The first paper consists of a brief account of the Kimberley 

 and De Beers mines in 1886, and contains quotations as to the 

 geology of the mines and neighbourhood from the writings of 

 E. J. Dunn, while reference is made to the accounts given by 

 Dr. Cohen, Thomas Stow, Hudleston, Prof. Maskelyne, and Dr. 

 Flight. Prof. Lewis suggests the shales in which the diaman- 

 tiferous pipe lies as the source of the carbon now appearing as 

 diamonds. The age of the pipes is given as Upper Triassic 

 or Post-Triassic. 



The diamantiferous rock is described from sections as " a 

 volcanic rock, composed mainly of olivine, and containing no 

 felspar, i.e., a peridotite." 



The second paper is much longer. It begins by referring to 

 the resemblance of the Kimberley rock to one found in Elliott 

 Co. Kentucky, and gives a detailed account of the various 

 minerals found in the former. 



Prof. Lewis's conclusions are that the diamantiferous rock 

 is a true igneous lava and not an ash or tuff, and the diamond 

 is one of the original constituents of the rock. He introduced 

 the name Kimberlite to mark the distinct nature of this type 

 of rock from all others known. 



The concluding section by Prof. Bonney deals with the 

 varieties of " Kimberlite " from the United States, one of which 

 occurs at Syracuse, N.Y., and another near Willard, Elliott Co. 

 Kentucky. The former occurs as a dyke cutting through lime- 

 stone, the latter as wedge-like projections from a dyke between 

 the strata of the coal-measures. Prof. Bonney regards the 

 American rocks as "a little more like a porphyritic igneous 

 rock than those which he has seen from Kimberley." 



G. S.C. 



