27S X AT URAL SCIENCE [October 



The Origin of the Diamond. 



Papers and Notes on the Genesis and Matrix of the Diamond. By the late 

 Henry Carvill Lewis : Edited from his unpublished MSS. by Professor T. G. 

 Bonney, D.Sc, etc. London: Longmans, Green & Co., 1S97. Pp. 72, with 2 

 plates and 35 figs. Price, 7s. 6d. 



The late Professor Carvill Lewis was much interested in the remark- 

 able occurrence of the diamond at Kimberley, and shortly before his 

 death devoted considerable care to a study of the rock in which the 

 diamonds are found. He communicated two papers on the subject 

 to the British Association in 1886 and 1887 with the intention, 

 apparently, of continuing his researches and of writing a book on 

 the general question of the origin and occurrence of the diamond. 

 This work was cut short by his premature death, and the present 

 volume contains merely the full text of the two British Association 

 papers, with a few notes and an appendix by Professor Bonney. 



The most diverse opinions have been held regarding the nature 

 and origin of the peculiar rock, known as " Blue Ground," in which 

 the diamonds of Kimberley are embedded. A vertical column of 

 serpentinous material, unlike anything else upon the surface of the 

 earth, extending to an unknown depth, and of enormous dimensions, 

 it was supposed by some to be the neck of a volcano, by others to be 

 a volcanic breccia due to a sort of mud eruption. The object of Pro- 

 fessor Lewis's papers is to show, by an elaborate and minute 

 microscopic study of the rock itself, that it was a true igneous lava, 

 or, to use technical language, the ' Blue Ground ' was, according to 

 him, a porphyritic volcanic peridotite or basaltic structure, an olivine- 

 bronzite-picrite-porphyrite, rich in biotite (now very much de- 

 composed), and for this remarkable rock he proposed the name 

 " Kimberlite." 



The chief argument upon which his conclusions were based is that 

 in tw T o American localities, namely at Syracuse, New York, and in 

 Elliott County, Kentucky, a precisely similar rock occurs, though 

 without diamonds, and is there obviously an eruptive rock. Professor 

 Bonney 's appendix consists of a detailed description of these two 

 rocks, which he also regards as practically identical with "Kimberlite," 

 although he does not quite agree with Professor Lewis's views con- 

 cerning the origin of the latter. 



It has generally been supposed that the diamonds in the blue 

 ground were either caught up from some underlying rock or are due 

 to the fusion of the carbonaceous shales through which the blue 

 ground passes, or are decomposition products. Professor Lewis em- 

 phatically states his opinion that the diamond is an essential 

 constituent of the rock like any of the other minerals which if 

 contains; in this view he probably stood alone at the time of his 

 death, and it is not one which lias been generally accepted since. 



It cannot be said, therefore, that these papers contribute much 

 to our knowledge of the origin of the diamond; they constitute a 

 careful description of the rock in which the precious mineral occurs 

 and establish the existence of a similar rock elsewhere, but no reason 

 is suggested why it only contains diamonds at Kimberley. 



Professor Bonney has done well in giving these posthumous 

 papers to the world, and has considerably enhanced their value by 



