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THE ORIGIN OF THE DIAMOND 
PAPERS AND NOTES ON THE GENESIS AND MATRIX OF THE DrAmonp. By the late 
Henry Carvill Lewis: Edited from his unpublished MSS. by Professor T. G. 
Bonney, D.Se., etc. London: Longmans, Green & Co., 1897. 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, 
, 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 two 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 ne latter. 
Tt 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 it 
contains; in this view he probably stood alone at the time of his 
death, and it is not one which has 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 
