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Full text of "Papers and notes on the genesis and matrix of the diamond"

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HENRY GARVILL LEWIS, BORN 1853. 
PROFESSOR OF CHEMISTRY AT THE PHILA- 
DELPHIA ACADEMY OF SCIENCES, 1880; at 
HAVERFORD COLLEGE, 1883. 
FOR SOME TIME EDITOR OF THE MINERAL- 
OGIGAl' DEPARTMENT OF THE AMERICAN 

NATURALIST . 

AUTHOR OF MANY VALUABLE PAPERS ON 
GEOLOGY AND PETtWLOGY 






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THE DIAMOND 



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PAPERS AND NOTES 

ON Til K 



GENESIS AND MATRIX 



OF 



THE DIAMOND 



BY THE LATE 

HENEY CABVILL LEWIS, M.A., F.G.S. ' 

e • 
PROFESSOR OF MINERALOGY IN THE ACADEMY OF NATURAL SCIENCES, PHILADELPHIA 
PROFESSOR OF GEOLOGY IN HAVERFORD COLLEGE, U.S.A. 



EDITED FROM HIS UNPUBLISHED MSS. 

BY 

PROFESSOR T. G. BONNEY 

D.Sc, LL.D., F.R.S., ice, 



LONGMANS, GREEN, AND CO. 

30 PATERNOSTER ROW, LONDON 
NEW YORK AND BOMBAY 

1897 

l A 1 1 rig lit s reserved 1 



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i 



* 



NOTE 

Mrs. Carvill Lewis gladly avails herself of this oppor- 
tunity to express her indebtedness and gratitude to Professor 
T. G. Bonney for his kindness in arranging and editing 
the papers and notes contained in this book, in accordance 
with the wishes of the late Professor Henry Carvill Lewis, 
whose desire it was that his researches on the origin and 
matrix of the diamond should be given to the scientific 
world. 



F 



M 



PREFACE 



*-. * 



A few words of explanation are necessary in order to 
indicate my connection with this book and what has or 
has not been attempted in preparing it for publication. 
Shortly after the death of Professor Carvill Lewis in July 
1888, in accordance with directions given during his last 
illness, the manuscripts of his two papers on the diamond- 
bearing rocks of Kimberley, communicated to the British 
Association at the meetings in 1881) and 1887 respectively, 
together with the specimens on which he had worked and 
a number of miscellaneous notes, were given by Mrs. 
Lewis to Professor G. H. Williams of the Johns-Hopkins 
University, who had kindly promised to carry out his late 
friend's desires by preparing the incomplete material for 
publication, as soon as his other duties and engagements 
permitted. But the pressure of these was so great that an 
opportunity had not been found when he too was taken 
away from this world by the same disease (typhoid fever) 
which had proved fatal to Professor Lewis. As I havo 
been for many years a student of the structure and history 
of olivine rocks and serpentines, I had felt great interest in 
the papers to which I had listened at Birmingham and 
Manchester, and thought it would be most unfortunate if 
the numerous careful and minute observations which they 



viii PBEFACE 

contained were much longer delayed in publication, or, 
perhaps, were even lost to science. Accordingly I informed 
Mrs. Lewis that if she would entrust the manuscripts to 
me I would do my best to arrange them for publication, 
stating at the same time that I could not attempt more 
than to act as an editor to the materials which had 
been left by her late husband. From some of the docu- 
ments it was obviously his intention, had his life been 
spared, to have carried on his researches and to have made 
additions to the original papers so as to bring the subject 
down to the date of publication. But this task, as I told 
Mrs. Lewis, I could not undertake. Parts of the subject 
lay rather outside my usual lines of work, so that very 
much time would have had to be spent in hunting through 
the geological, and more especially mineralogical, literature 
of the last eight or nine years on the chance of finding 
something throwing light on the questions treated by 
Professor Lewis. As the hours which I can devote to 
prosecuting my own investigations are none too numerous 
already, I was unable to undertake what w T ould have been 
of little profit and hardly any interest. To me no work is 
so irksome as that of searching through periodicals on 
the chance of lighting upon some contribution — possibly 
in itself of little value— to the literature of a subject. 

Thus the two papers, forming the first and second 
sections of this book, are printed very nearly as they were 
left by Professor Lewis. The references have been tested 
and corrected, and a few changes have been made here 
and there in phrase or in the order of sentences. These 
changes, however, are merely editorial, such as the author 
himself would have most probably made in finally revising 
his manuscript for the press. Accordingly the statements 
printed and the results given represent his views, at 



PREFACE i\ 

any rate in 1887, and, so far as I know, at the time of his 
death. Of the third section nothing had been written ; the 
materials consisted only of some very brief 'jottings ' and 
a small set of rock specimens. The latter, however, 
appeared to me to have such an important bearing on the 
subject of the first two sections that I have drawn up a 
statement of the facts concerning them from such literature 
as I have found, and have written some brief descriptions 
of the structures, macroscopic and microscopic, of the 
specimens themselves. 

In addition to the above-named materials, Professor 
Lewis left numerous notes on the occurrence of diamonds 
in other countries, and on various matters bearing more or 
less indirectly on the subject of the two papers. Two 
pocket-books also w r ere placed in my hands, containing 
memoranda of a journey through some districts in the 
United States where diamonds had been, or were said to 
have been, discovered. From these I compiled two other 
sections, weaving the materials of the latter, after con- 
siderable condensation, into a continuous narrative. 
The manuscript was set up in type, but Professor Eosen- 
busch, to whom the whole of the proofs were submitted, 
was of opinion that they would not augment the value of 
the earlier part of the book, because the notes on localities 
were obviously incomplete, and the journeys were more 
negative than positive in their results. Moreover, many of 
the facts recorded had already, owing to the lapse of time, 
become incorporated into literature readily accessible to 
students. I had myself felt a like misgiving, but, for a 
reason which will appear below, felt bound to alter or to 
cancel as little as possible. But when fortified by such 
an authority on this special topic as Professor Rosenbusch, 
in whose laboratory at Heidelberg much of the work 



x PREFACE 



embodied in the first and second section had been done, I 
had no hesitation (with the concurrence of Mrs. Lewis) in 
following his advice. So this portion has been cancelled, 
and as the book now stands it comprises all the manuscript 
that Professor Lewis had left in a fairly complete state, with 
a little supplementary work which has a very direct bearing 
on the subject of his two papers, and for which he had 
collected specimens. 

Several months elapsed, owing to various circum- 
stances, before Mrs. Lewis could place the late Professor's 
manuscripts and the other materials in my hands. In the 
interval Sir J. B. Stone, M.P., when I was a guest at 
Erdington Grange, his pleasant home near Sutton Cold- 
field, showed me a collection of specimens which he had 
obtained during a recent visit to the Kimberley mines. 
Among these were two lumps of the diamond-bearing rock, 
each as large as three or four ordinary cabinet specimens, 
and in a much better state of preservation than any which 
I had previously seen. One of these he kindly gave to me, 
asking me to examine its structure, and allowing me to 
make use of the other materials in his possession. Some 
microscopic sections were prepared from this specimen, 
and, in addition to others already in my collection, the gift 
of Professor Boyd Dawkins, I had the advantage of studying 
one or two small but well-preserved pieces of the rock, which 
had been presented to Miss C. A. Raisin by C. J. Alford, Esq., 
as well as others kindly lent to me by the late Professor 
A. H. Green. 1 The results of these studies were published 
in the Geological Magazine for 1895 (pp. 492-502) in a 
paper jointly written by Sir J. B. Stone, Miss C. A. liaisin, 



i J> H Y lied aftCr a Sh ° rt ilIneSS ' the result ' l fear ' of overwork, in August 
18J0 A good geologist and a most unselfish man, multis ille bonis ilcUU, 
occidit ! 



PBEFACE 



M 



and myself. Our conclusions in one respect differed a little 
from those expressed by my lamented friend Professor 
Lewis — viz. as to the origin of the diamond -bearing rock 
to which he has given the name Kimberlite. Its precise 
nature is undoubtedly very difficult to determine. It 
differs from any rock, whether peridotite or serpentine, 
known to me, and my experience, especially in regard to 
the latter, is a rather large one, Its structure is hardly 
such as I should expect to result from the hydration of a 
glass, the chemical composition of which nearly corre- 
sponded with that of olivine, and it seems to me improbable 
that the material would have remained in a glassy con- 
dition throughout pipes or necks of such great size, which 
also have now been excavated to a considerable depth. 
Olivine is not a very fusible mineral, and vitreous peridotites 
are even more rare and limited in extent than taehylites ; 
indeed, I am doubtful whether I have ever really met 
with one. Some, indeed, of the fragments in these 
diamond-bearing breccias (for, whatever may be the ex- 
planation, they undoubtedly exhibit a brecciated structure) 
may — probably do — represent either a glassy or at any 
rate a very compact form of peridotite (now converted into 
serpentine) ; but I regard them, together with the olivine, 
augite, mica, garnets, and other large minerals (not ex- 
cluding the diamonds) as true c fragments,' like the pieces 
of shale which are sometimes found associated with them, 
produced by the explosive destruction of more coarsely 
crystalline rocks of earlier consolidation, and not the result 
of a fluxional movement in a magma which had previously 
reached a stage of partial separation and incomplete con- 
solidation, and had in addition incorporated fragments of 
overlying rocks in its upward progress. The subject, how- 
ever, is one of great difficulty, and it may be that Professor 



I 






xii PREFACE 

Lewis' explanation is the more correct one. I refer to my 
own conclusions only because they were formed quite inde- 
pendently ; for at that time abstracts merely of Professor 
Lewis' papers had been published, and from these I had 
formed the impression that the name ' kimberlite ' designated 
the serpentinous fragments which were embedded in the 
breccia, and not the rock itself. But whatever be the 
ultimate result of that part of the inquiry, this would not 
necessarily affect my friend's views as to the genesis of 
the diamond — viz. by the action of an extremely basic rock 
upon carbonaceous material — or diminish the value of his 
elaborate researches into the structure and mineral com- 
position of its matrix. 

There remains only the pleasant duty of returning, on 
behalf of Mrs. Lewis and for myself, most hearty thanks 
to two friends : to J. J. H. Teall, Esq., F.K.S., who has 
most kindly taken the admirable micro-photographs of the 
slices of the Kimberley and the Kentucky rock, in order to. 
illustrate this work ; and to Professor Rosenbusch, who has 
been so good as to read and criticise the proofs. Only 
those who, like the editor, have learned from experience of 
his books the rich stores of his mineralogical and petro- 
graphical knowledge can fully appreciate the value of his 
generous assistance in putting on record some of the 
work produced by one who studied in his laboratory at 
Heidelberg. 

T. G. BONNEY. 



CONTENTS 



SECTION 



I. PAPER READ IN 188(5 



I'AGE 



II. PAPER READ IN 1887 



10 



III. KIMBERLITE FROM THE UNITED STATES 



■ • 



58 



NOTE 



r>8 



INDEX 



. 70 









LIST OF ILLUSTRATIONS 



PLATES 



PLATE I 



Fragment of the Diamond-hearing Hock 
(Natural Size) ...... 



FROM KlMBERLEY • 

Frontispiece 



This specimen was obtained at the diamond workings by Sir J. 13. Stone, 
M.P., F.G.S., in 1894, and given by him to the editor. It came from the De 
Beers mine, and from the deepest level then worked — viz. rather more 
than 1,000 feet. It is a characteristic but slightly coarse variety of the 
rock, in very good preservation, exhibiting very well its peculiar brecciated 
structure. The largest fragment is a rather decomposed compact serpen 
tinous rock ; the smaller grains are mostly mineral — partially serpentinised 
olivines and pyroxenes, with a few flakes of mica, which, however, cannot 
be distinguished in the plate. 



PLATE 11 

Microscopic Structure of Part of a Slice err from the 
Specimen of Kimberley Hock represented in Plate I. 
(x 22 Diameters) . . . (Upper Figure) . Tofaccp.1'2 

X early in the centre of the figure is a rather rounded grain of mica, showing 
the usual clea\age, and bordered by alteration products (p. 25). The 
large grain, part of which is shown on the S.W. 3ide, is most probably 
enstatite, serpentinised externally, the difference of tint in the border 
corresponding with a slight difference in the character of the replacinig 
mineral. The smaller grain near the mica (to the S.E.) probably is 
also enstatite, but completely changed ; others are serpentinised olivine, 
but larger grains of this mineral, only changed at the border, occur in 
other parts of the slice. The grain partly included in the figure and 
to the W.N.W. of the mica is very compact in structure, seemingly 
composed of minute serpentinoits materials, and possibly may be a rock 
fragment (? of a glassy peridotite). The separate mineral grains, as will be 
seen, decrease in size till they become indistinguishable from the granular 
matrix of serpentine, calcite or dolomite, iron oxide, perovskite, &c, 



XVI 



LIST OF ILLUSTRATIONS 



PLATE II 

Microscopic Structure of Part of a Slice cut from a Specimen 
of klmberlite from elliott county, kentucky ( x 28 dla- 
meters) ; see page 06 . . (Lotver Figure) . To face p. 12 

To the S.S.E. of the centre and rather nearer to the edge is a grain of biotite, 
showing cleavage planes, and slightly bordered as above. The large grain, 
partly included to the S.S.W., is olivine, almost wholly converted to 
serpentine. The remaining grains are the same mineral in various stages 
of change, but the rather large one just N. of the centre possibly may be 
enstatite. The matrix consists, as before, of a mixture of granules of 
serpentine, iron oxide, perovskite, Arc. 



ILLUSTRATIONS IN TEXT 



» -• 



fk;. 

1. Du Torr's Pan Mine, 1885 . 

2. De Beers Mine, 1885 .... 

3. Olivine Crystal seen parallel to xPx 

4. 5. Corrosion Cavities 

6. Tremolite ...... 

7. Two Olivine Crystals 
8-10. Alterations of Olivine . 

11-13. Kutile in Olivine 

14. Rutile 

15, 16. Rutile with Titanic Iron 

17. Olivine and Diopside from Kentucky Peridotite 

18. Enstatite and Biotite . 

19. Perovskite 

20-23. Twinned Perovskite . 

24. Twinned Perovskite .... 

25. Twinned Perovskite 

26. Inclusions in Perovskite 

27. Titanic Iron in Perovskite . 

28. 29. Perovskite surrounding Olivine . 

30. Perovskite 

31. Cyanite 

32. Minute Diamonds .... 

33. Microscopic Section of Kimberley Peridotite . 

34. Shale Fragment filled with the Ground- mass 

35. Shale Fragment surrounded by Calcite . 



PA(.E 

3 
K 
13 
13 
15 
15 
16 
16 
17 
17 
17 
17 
29 
30 
31 
32 
33 
33 
34 
36 
39 
41 
42 
46 
46 



SECTION I 

ON A DIAMOND-BE ABING PEBIDOTITE AND ON 

THE HISTORY OF THE DIAMOND 

By H. CABVILL LEWIS, M.A., F.G.S. 

(Read at the Meeting of the British Association at Birmingham, 1886 ') 



The discovery of diamonds at Kimberley, South Africa, has 
proved to be a matter not only of commercial hut also of much 
geological interest. Here the diamonds occur under con- 
ditions which are unlike those of any other known locality, 
and are worthy of special attention. 

The first diamond was found in South Africa in 1807, 
when a large specimen was picked out of a lot of rolled 
pebbles gathered in the Orange River. This led to the 
river diggings in the Orange and Vaal rivers, which con- 
tinue to the present time, but are now only worked at three 
or four points. 

In 1870, when perhaps 10,000 persons had gathered 
along the banks of the Vaal River, the news came of the dis- 
covery of diamonds at a point some 15 miles away from the 
river where the town of Kimberley now stands. These were 
the so-called * dry diggings,' which at lirst were thought to 
be alluvial deposits, but have proved to be volcanic pipes 
of a highly interesting character. In 1871 four mines 
were discovered in close proximity to Kimberley, all of 
which have since become famous. They are known as Du 
Toits Pan, De Beers, Kimberley, and Bulfontein mines, all 



1 This date must be understood as limiting the phrases applying to time 
throughout the paper. 



B 



2 ON A DTAMOND-BEABING PEBIDOTITE AND 

of which could be enclosed by a circle 3i miles in diameter. 
The mines lie at the northern end of a great plateau, 
known as the Upper Karoo Plateau, which extends from 
the Bokkeveldt mountains at the Cape of Good Hope to the 
border of the Transvaal Republic,, varying in elevation 
from 2,700 to 6,000 feet above sea level. 1 The four princi- 
pal mines at Kimberley, at an elevation of about 3,1)00 
feet, are close to one another. The two principal mines in 
the Orange Free State (Koftee-fontein and Jagers-fontein) 
lie S.E. of Kimberley, the former 30 miles, the latter 00 
miles distant. 

In 1872, 30,000 persons had assembled about the four 
mines, and other mines were soon discovered in the neigh- 
bouring territory. At the present time, 15 distinct diamond 
mines (dry diggings) are known in Griqua Land, Urot and 
the adjoining Orange Free State ; none of the others, how- 
ever, as yet equal in richness the four great mines first 
discovered. These four all have the same geological 
structure, each being a separate pipe; and all are re- 
markably rich in diamonds. It has been estimated that 
since the opening of these mines more than six tons of 
diamonds 2 have been extracted from them, being probably 
greater than the total combined previous production of ail 
the other mines in the world. It was soon discovered that 
these pipes went down vertically to an unknown depth, 
penetrating the surrounding strata. 

The diamond-bearing material first excavated was a 
soft yellowish friable substance, readily crumbling when 
exposed. At the depth of about 100 feet it became darker 
and harder, and finally acquired a slate blue or dark green 
colour, resembling some varieties of serpentine. This is 
the well-known ■ blue earth ' of the diamond mines, which 
proved to be richer in diamonds than the wholly deeom- 

1 Cape of Good Hope Official Handbook, 1886, p. 169 

*r , „ T * K , e r unert ' Ca ^ °f Good H °& Official Handbook, 1886, p. 212T 

Moulle, 'Mtinoire sur la fftologie e£n£rale M an* w. , • i- 

, ■,,.* . i a j. 7 ° M-'itiaie et .sin Jes mines de diamauts 

cle 1 Afnque du bud,' Ann. des Mines, vii. 1885 p 193 



ON THE HISTORY OF THE DIAMOND 3 

posed and weathered portion first penetrated, and called 
< yellow ground.' This ' blue earth ' or ' blue ground ' is 
taken out of the mine and exposed to the sun, and it is 
then capable of being readily crashed and washed for the 
extraction of its included diamonds. The ' blue ground ' 
is greasy to the touch like serpentine, and is full of enclosed 
fragments of slate and other substances. It has been found 
to become harder and more stony the deeper it is pene- 
trated, and to continue vertically downwards to an un- 
known depth. The deepest sinkings in Kimberley mine 
are now GOO feet below the surface, still in the same 
compact material. 1 At this depth the true nature of the 
diamond-bearing substance is more clearly apparent than 



— £ 




Fk; 1 — Du Toit's Pan Mine, 1885. (Sketch by Professor Lewis from the Colonial Exhibition, 

1886). I, debris ; 2, yellow shale ; 8, black shale ; 4, diamond-bearing ruck- 
it was when the workings were carried on in the more de- 
composed material. Quite recently, both in the Kimberley 
and De Beers mines the remarkable rock has been reached 
which forms the subject of the present paper. 

The first scientific publication regarding the matrix of 
the Kimberley diamonds appears to be that of Prof. E. Cohen, 
in 1872, 2 and, in England, of Mr. E. J. Dunn, in 1873.' 5 
Before that date, however, Mr. CI. W. Stow 4 and Dr. John 
Shaw' had described the general geology of the region, and 



1 They have been carried to a very much greater depth since 1886.— 
rp # Q. t i3. '-' Neues Jahrb. 1872, p. 857. 

3 Quart. Journ. Oeol. Soc. xxx. 1874, p. 54. 
1 Ibid, xxviii. ls7"2, p. 3 (of. Oeol Mag, 1871, p. 41)). J Ibid. p. '21. 

u 2 



4 ON A DIAMOND-BEARING PEBIDOTITE AND 

Prof. T. Rupert Jones and Mr. Thos. Davies had identified 
a number of the minerals occurring associated with the dia- 
mond. Mr. Dunn has described the occurrence so well that 
I cannot do better than quote some extracts from his paper. 1 

' The conditions under which diamonds occur in South 
Africa are quite different from those of every other known 
locality, and are so unusual as to deserve the earnest 
attention of all geologists. 

' At the junction, and back for a distance of from one 
to several feet, the edges of the shale are bent sharply 
upwards. The contents of these "pipes' in the shale arc; 
the same in all cases, and show distinctly that they are of 
igneous origin. The base is more or less decomposed 
gabbro (?) or euphotide (?), through which are scattered 
particles, fragments, and huge masses of shale, nodules 
of dolerite, occasional fragments of chloritic schist, 
micaceous schist and gneiss. The principal foreign in- 
gredient is the shale, which in many places, particularly 
at Colesberg Kopje, is thoroughly comminuted, forming a 
breccia with euphotide (?) as a base. Where large masses of 
shale occur, the lines of the bedding, as might be expected, 
are not horizontal, but lie in all directions. 

' For a depth of from 30 to 40 feet, cracks, joints, and 
irregular cavities filled with red sand from the surface 
penetrate; with the sand, and showing that it has come 
from the surface, are fragments of ostrich egg-shell, small 
rounded grains of chalcedony, agate, &c, identical with the 
same substances mixed with the surface soil. 

< At 180 feet, the greatest depth so far attained, the 
rock becomes compact, tough, and shows the original 
texture, though the ingredients are altered, notably the 
pyroxene or augite into bronzite. 2 

' The entangled blocks of shale and sandstone are fre- 
quently altered, the latter sometimes into quartz rock. 



1 Quart. Jonrn. GeoL Soc, xxx. 1874, p. 54. 

2 Probably diallage is here meant ; the name bronzite, which formerly 
was used somewhat vaguely, being now restricted to a rhombic pyroxene.- 
T. G. B. 



ON THE HISTORY OF THE DIAMOND 



5 



1 A very well-known fact on the diamond-fields, and one 
rather in favour of the euphotide (?) being the mother rock, 
is that each of the pipes furnishes diamonds easily distin- 
guishable from those found in the others. Bulfontein pro- 
duces small white stones, occasionally specked and flawed, 
but very rarely coloured; while l)u Toits Pan, within half 
a mile, seldom yields other than coloured stones. So well 
marked arc the characteristics of the diamonds from the 
various diggings, that diamond buyers can generally tell by 
the appearance of a stone the locality from which it has come.' 
Mr. Dunn's paper was followed in the same year by a de- 
scription of the microscopic character of the diamond-bearing 
rock by Professor N. S. Maskelyne and Dr. W. Flight. 1 

The specimens examined and analysed by them were 
unfortunately all decomposed more or less, none coming 
from a depth greater than 180 feet. They identify a 
bronzite (two varieties, one bright green, one buff coloured), 
a variety of smaragdite, garnet, ilmenite, a diallage (much 
altered) and a mica-like mineral. Opaline silica, occasion- 
ally hyalite, sometimes resembling hornstone, is dissemi- 
nated through the rock ; the mica-like mineral is described, 
analysed, and named vaalite, it being regarded as an out- 
lying member of the vermiculitc family ; the smaragdite, 
in brilliant greyish green fragments, green bronzite and a 
much altered bronzite, resembling that in the meteorite of 
Breitenbach, are also analysed, as is the rock of Bulfontein. 
This gives (water being undetermined) :— 

CaC0 8 59 ' G25 

MgC0 3 4-972 

FeC0 3 ^ oir> 

SiCX, ..... 

Al 2 6 3 

FeO 

MgO ..... 

Cat) ..... 



20-700 
0*558 
4-296 
5-799 
0-524 

<H)'4S5 



1 Quart. Joum. Geol Soc. xxx. 1874, p. 406. 



6 ON A DIAMOND-BEARING PEBIDOTITE AND 

Additional particulars, of which a brief summary is 
subjoined, are supplied in more recent papers by Mr. 
Dunn, 1 which are founded upon facts brought to licht 
by fresh excavations. 

The bedding of the black shales surrounding the mines 
is turned upwards at the edges of the pipe. These shales 
are very combustible and carbonaceous ; in one part of 
Kimberley Mine, where accidentally fired, they have 
smouldered on for eighteen months. The shales extend 
at least forty miles away, underlying the whole district. 
Diamonds are most abundant where the pipe is surrounded 
by shales. The author suggests that the carbon for the 
diamonds was supplied by these shales. If so, the atmo- 
sphere would be the original source of the diamond, for 
the plants absorbed carbonic acid from the air, and their 
remains made the shales carbonaceous. 

These shales belong to the Karoo beds. In Camdebro 
anthracite occurs in these beds; perhaps the result of 
distillation, due to a large dyke which underlies the anthra- 
cite. 

The dyke-like masses 2 at De Beers differ from the 
main mass only in being finer grained and less readily 
decomposed. They are two to three feet thick, and cut 
through the pipe and the shales and dolerite in all direc- 
tions. Mr. Dunn also shows that the pipes must be more 
recent than the dolerite sheets, for the rudely tabular 
dolerite is tilted up at 40° at the wall of the pipe. In- 
cluded masses of dolerite also occur in the pipes, which 
at Bulfontein have been rounded by attrition into boulder- 
like masses. 

Among recent papers on the diamond regions must be 



p. m. lfarL Journ ' GcoL Soc ' xxxiii ' 1877 ' p - 879 - Ibhl xxxvii - ism. 

half fn?/ r0/ " SS ° r ^ ThG S °- Called **" ftt De ***** «■ ***** 
Dow t iJn fa f ne ' ej a,ned P ftrts of the «■« which are not decomposed 

fhe bU Zn7 V tlC BUrfftCe ' bhdlS ' CharCOa1 ' **» have e " te '« ** 



ON THE HISTOBY OF THE DIAMOND 7 

mentioned those of Prof. E. Cohen, of Mr. Hudleston, and 
of Mr. Dunn. Mr. Hudleston ' holds that the matrix of the 
diamond was a sort of volcanic breccia, which was made 
hydrous at a considerable depth and ejected in a wet 
etate accompanied by steam, like the product of a mud 
volcano. The earlier theories as to the origin of the 
diamond have, in the light of new facts, cpiite given way 
to the theory that the diamonds belong to and arc part of 
the matrix in which they lie, and that this matrix is in 
some way of volcanic origin, either in the form of mud or 

ashes or lava. 

As the geology of the region has been described by 
many observers, it may suffice to say that the diamond- 
bearin" pipes penetrate strata of Triassic age which arc 
known°as the Karoo beds. Griesbach » and Stow 3 in 1871 
showed that this Karoo formation was penetrated by great 
interstratihed sheets of so-called dolerite, melaphyre and 
amygdaloidal melaphyre, and that below the series of 
stratified rocks fundamental clay slates and gneisses or 
granite occurred, which latter came to the surface in Natal 
and the adjoining regions. The intrusion of the dolerite 
sheets in the Karoo beds is held to have occurred in a 
subsequent part of the Triassic period known as that 
of the Sternberg beds.-' As Professor Rupert Jones 5 and 
others have shown, the Kimberley shales belong to the lower 
Karoo formation. The diamond-bearing pipes penetrating 
and enclosing fragments of all these formations are thus 
clearly of upper Triassic or post-Triassic age. 

I now come to the description of the rocks which, 
through the courtesy of Mr. T. Hedley, in charge of the 



1 Proc. Qeol. Assoc, viii. 188J5-4, p. 65. 

« C. L. Griesbach, ' On the Geoloyy of Natal,' Quart. Journ. Geol. hoc. 

" 1Q71 n Vl 

XX ™ G. W.' Stow,' • On some points in South African Geology, 1 Quart. Joum. 

Qeol Soc. xxvii. 1871, p. 497. 

* Cape of Good Hope Official Handbook, 1886, p. 8d. 

& Mining /om^L886, p. 771. 



1 

j 

i 

I 

- 



8 ON A DIAMOND-BEARING PEBIDOTITE AND 



diamond exhibit at the Colonial Exhibition, I have been 
able to examine. They come from De Beers Mine, and 
having been found at a greater depth and in a much less 
decomposed condition than the specimens primarily ex- 
amined, it has become possible now, for the first time, to 
determine the exact nature of the matrix of the diamond. 

The rock occurs in two types, one not bearing diamonds, 
the other diamantiferous, and the distinction between them 
is suggestive. Both occur in the same mine, and are dark, 
compact, heavy rocks, closely resembling one another, and 
differing mainly in the fact that one is free from en- 



_ I * 





Pro, J.— De Beers Mine. 1885. (Sketch by Professor Lewis from tlie rtnlnnl.1 i\ i 
Mtion, 1886.) 1, basalt : 2, shale ; 3, hard ground ! 4, floato? r 4 true eranui 
rock, with more broimte, no enclosures.no diamonds) ; ^dlamond-bearlngrook 



closures of foreign substance, while the other is full of frag- 
ments of shale and other impurities. It is the latter which 
is diamantiferous. 

A section of either of these shows that we have to do 
with a volcanic rock, composed mainly of olivine, and con- 
taining no felspar, i.e., a peridotite. I will describe first 
that which is free from inclusions, known as Hard Wack 
Floating Reef (the word 'reef meaning anything which 
is worthless). It occurs deep down in the mine° and is 
a massive black rock. Microscopic examination shows 
abundant grains of olivine in a remarkably fresh condition- 
many of them are rounded, but others show crystalline 
laces. That olivine is rounded is a common feature, both 
in volcanic rocks and in meteorites. The cleavages accord- 



ON THE HISTORY OF THE DIAMOND 







ins to odP<£ and a: Pod are unusually well marked, that 
according to oo P oc being often in straight lines almost 
as good as in felspar. Olivine is known to occur in rocks 
in three different habits, according as the rock is granular, 
porphyritic, or a crystalline schist, as Eosenbusch 1 has well 
described. The rock in question contains olivine, with the 
form belonging to porphyritic rocks. The distinct crystalline 
shape has been altered by subsequent corrosion. Olivine is 
the main ingredient of the rock, all other minerals being 

accessory. 

Of these the principal arc enstatite and biotite. The 
enstatite is clear, not pleochroic, and is readily determined 
by its parallel extinction ; the biotite is in crystals, which 
are usually rounded by corrosion, as is indicated by the 
black rim which often surrounds them. Similar rims are 
well known around the biotite of many andesites, trachytes, 
and related rocks. The black rim is shown to be made of a 
mixture of magnetite and augite, and is thickest when the 
ground mass is holocrystalline, and thinnest when most 
glassy. The very thin rims here argue a glassy base. The 
biotite, as in peridotites and nepheline-basalt, is usually 
twinned after the law of Tschermak. 

Serpentines with garnet occur as dykes in the ^ aal 
River. Dr. J. Shaw speaks of serpentines,- and Professor 
T. R. Jones of garnets, in Vaal River gravels. 3 Dr. 
Shaw ' also states that dykes cross the Vaal River and 
make rapids. Garnets abound in these gravels, also 
tourmalines, talc, and mica. 



I 



1 



1 Mikrosk. Physiogr. 2 e AuH. Bd. i. 1885, p. 410. 

2 Quart. Joarn. OeoL Soc. xxviii. 1*7'2, )). 4 2'2. 

3 Ibid. p. 18. 4 Ibid. p. 21. 



10 THE MAT BIX OF THE DIAMOND 



SECTION II 

THE MAT MX OF THE DIAMOND 

By H. CAEVILL LEWIS, M.A., F.G.S. 
(Bead at the Meeting of the British Association at Manchester, 1887) 

At the last Meeting of this Association l I had the honour 
of giving a short description of the remarkable rock which 
forms the matrix of the diamond in South Africa. Since 
then, as I have received fresh material, it has been possible to 
study it carefully, both microscopically and chemically, and 
to compare the geological features of Kimberley with those 
of other diamond localities in various parts of the world. 

Without repeating what was then said, I will merely 
remind you that the diamond-bearing rock was shown to 
be an eruptive neck of post-Triassic age, penetrating and 
enclosing fragments of Karoo shales, and that this rock is 
a porphyritic peridotite of peculiar structure, closely ana- 
logous to a similar rock in Elliott Co., Kentucky. 2 

The rock, which was obtained from a depth of about 
500 feet, is much less decomposed than the material 
usually obtained in the diamond mines, and both its 
composition and structure can be readily studied under the 
microscope. 

It is a dark-green heavy rock, resembling a dense 
serpentine, in which one sees with the naked eye glistening 
plates of brown biotite, small deep-red garnets, and large 
dari^green^crystals or grains of olivine and bronzite. 

1 At Birmingham, 1880. Brit. Assoc. Report, 188(5, p. 007. 
* For a description of this rock, see Section III. 



THE MAT BIX OF THE DIAMOND 



11 



The last two minerals being of identical colour with the 
rest of the rock are not so conspicuous as the first two. 
Scattered through the whole rock are a large number of 
angular fragments of altered black shale. These are often 
so abundant as to give the rock a brecciated appearance. 
The rock takes a good polish, and, on such polished sur- 
faces, the olivine is clearly seen to be the predominating 
mineral, and to occitr in porphyritic crystals, lying in a 
ground-mass of serpentine. Traces of fluidal structure are 
also seen in polished specimens. The rock resembles, 
externally, certain dark picrites, like those of Tringenstein 
or Schriesheim, yet even its general appearance is different 
from that of any other known rock. 1 

The rock from Kentucky has the same characters, 
though containing less numerous foreign fragments. 

We now proceed to the more exact description of this 
reck. We will consider (1) the minerals of which it is com- 
posed, ( k 2) its chemical composition, (8) its structure, (4) its 
geological characters and significance. 

(1) Constituent Minerals 

The following minerals occur in the Kimberley rock, 
many of them being detected only under the microscope. 
Olivine, forming the larger portion of the rock, often 

quite fresh. 

Enstatite, chrome-diopside, smaragdite and bastite, often 

in fine green plates or crystals. 

Biotite, a very prominent ingredient. 

Garnet, common in bright red grains. 

Perovskite, abundant in microscopic crystals. 

Magnetite, chromite, ilmenite, picotite, common under 
the microscope. 

Apatite, epidote, orthite, tremolite, tourmaline, rutile, 
sphene, leucoxene (scarce and minute). 

1 So far as my knowledge goes, this remark, though written almost ten 
years ago, still holds good. A general idea of the aspect of the rock may be 
obtained from Plate I. T. G. 13. 



12 THE MATRIX OF THE DIAMOND 

Serpentine, caleite, zeolites, chalcedony, and tale ta 
decomposition products. Also an undetermined mineral 
probably cyamte, and finally diamond (scarce) 

Olivine -.-Olivine forms the most abundant constituent 
in the rock occurring m porpbyritic crystals or rounded 
grains, winch may attain considerable size. These crvsHl. 
are sometimes over a centimetre in diameter, though 
usually of smaller dunensions, and are sprinkled plentifully 
in a serpentinous base. The dark-green colour isCnearly 
hat of the whole rock that the olivine is not so conspicuous as 

bmS M: 8h, Tr n " thhl 8eCti0n8 ' it Is m ^ "or 
abundant Many of the crystals are comparatively fresh 

wzth the hardness and lustre of unaltered olivine ' Others 
are partly changed into serpentine, while others, agan e 
entirely replaced by serpentine. ° ' 

Except an occasional grain of n m»n A iii i 
rarely, enrtatiie, the fresh \&f k \, 1 ' », f£ 12 
wild enclosures. Occasionally bubbte-like inel, Jionl 

S, g T b T r ' iu ";r form - - | -'N*S! 

ca\ities. Ihese are often agsreffatAd fn^fiT^ • i 
a noSv -1 ^ " " ," 0t — — * the It J 

t'iz t rr ™ h „?t, aiso occiir '" "*■■ 

are seen to he n , ? , ° h 1 '°"' C1 ' """ MaBioni 

J*-. 1, has calle, ■-£^ > t£ifitfSS 



1 Quart. Joarn. Geo!. Soc. *li. iy 8 ; 



o> 1>. 382. 



THE MATBIX OF THE DIAMOND 



13 

ial 



mrallel to the brachypinacoid (ooP&), an optic axial 
rddx appearing in sections with the most marked 



bisectrix appear 
cleavage 





i rt «„ r,nv.in..i to t» P« and showing excellent cleavage along 

ff». 3. Olivine °S«*Z£g^vp. The Mlar bastitic mineral into which it is 

ccP-.,ana poorer < taivug e u« mg oleavage. A bisectrix occurs at right 

There are also secondary cleavages, and the usual 
irrecular cracks so common in olivine. 1 

Olivine has not been detected in the ground mass of 
this rock. It is usually in the form of crystals, more or 
less rounded and corroded, and even when completely 
changed to serpentine, the original crystalline form can 
generally be recognised. 

Corrosion cavities (the • embuchtungen of the Ger- 
mans) are sometimes seen in the olivines. 

The following are some of these : 





Fig. 5.— Corrosion oavitles 



Fio. 4.— Corrosion cavities 

Tzirkel, Mihrook. Beschaff. tor Min. 1878, p. 214. 



14 THE MATRIX OF THE DIAMOND 

The olivine alters by decomposition either into serpen- 
tine, or into tremolite, or into a bastitic iibrous mineral. 
The alteration into serpentine proceeds in the usual manner 
beginning at the outer edge and in cracks in the crystal, 
and gradually penetrating deeper, as new cracks are formed, 
until the change is complete. A homogeneous nearly 
isotropic serpentine is the final result. Fibrous serpentine 
or chrysotile also forms around the olivine grains, and in 
this case the chrysotile fibres stand more or less at right 
angles to the original faces of the crystal. The chrysotile 
is much more highly doubly refracting than the compact 
serpentine, which latter, when most dense, is often nearly 
isotropic. Another serpentinous mineral is faintly pleo- 
chroic in pale shades of green, and is, perhaps, more nearly 
related to bastite. 

Tremolite (fig. 6) in the form of asbestos occurs as a 
secondary mineral pseudomorphic after olivine. It fre- 
quently happens that while serpentinisat ; on begins at the 
outside of a crystal, fibrous tremolite begins growing within, 
finally forming a mass of asbestiform fibres surrounded by 
a zone of green serpentine. These asbestos fibres often 
grow partly parallel to the vertical axis, and partly parallel 
to the domes of the olivine. They are distinguished from 
other minerals by their high colour in polarised light, and 
by vertical fibres separated by partings or cleavages' like 
those which divide sillimanite, and by an obliquity of 
extinction at about 15°. They are perfectly colourless and 
non-pleochroic. A fibre may be compact in the centre or 
at one end, and at the other end may be fringed out into 
fine hair-like asbestos. 

In the second figure (7) two olivine crystals have grown 
side by side, their axes parallel. A thin green rim of 
serpentine surrounds each crystal. A round grain of olivine 
remains in each, and crystals of tremolite surround it 
Between the tremolite and the serpentine is a pseudomorphic 
mass of talcose substances, in which lie rutile needles 
parallel to the faces of the crystal. 



THE MATRIX OF THE DIAMOND 



15 



Another kind of alteration, rare in the Kimberley rock, 
but very common in the Kentucky variety, is into a 
peculiar finely fibrous substance of dark blue colour. 
The olivine is never wholly changed into this material, 
which appears only at the two extremities of a crystal or 
along cracks. The fibres always stand parallel to the 
cleavage planes of the olivine, and seem to be due to a 
finer splitting up of these cleavage planes until they 
become fibrous. This fibrous substance is faintly pleo- 



r 




Fig. 0. Diagrammatic, r, rutile needles; 
t>\ tremolite : eh, cbrysotile ; in, magnetite 
or chromite ; p, perov^kito 




Fig. 7.— Diagrammatic. .*, serpentine; 

//•, tremolite ; o, olivine ; r, rutile 



ehroic like bastite, and seems to be a new variety of that 
mineral. (It is seen only in the Kentucky rock.) Dr. 
llosenbusch suggested to me that it resembled the 'aerinite' 
of Lasaulx, 1 also a product of alteration. It will be more 
fully treated under the description of bastite. The un- 
usually perfect cleavage in the olivine is particularly well 
developed near the edges, where the fibrous substance is 
formed. This alteration is at the edges of otherwise 



1 Neues Jahrb. 1«7<*>, p. 352; Bull. Soc. Mln. de France, i. 1878, p. 125. 



16 



THE MATRIX OF THE DIAMOND 



perfectly fresh olivine, and appears to be an incipient stage 
of serpentinisation. 

The alteration into serpentine is shown in figures 8 
and 9 ; and into the chloritic mineral in figure 10. 






Fig. 8 



Fig. 9 
Alterations of olivine 



Fig. 10 



The most interesting result of the serpentinisation of 
the olivine is the production of secondary rutile. Rutile 
never appears in the fresh olivine, but as serpentinisation 
begins rutile needles form along the border of the de- 
composing olivine, their longer axes being parallel to 
the outlines of the original crystal. When serpentinisa- 
tion has proceeded so far that only an inner kernel of 
olivine remains, rutile needles may be formed all around 
this inner kernel, lying in the serpentine pseudomorph, 
not irregularly as if ordinary enclosures, but in fixed crvs- 
tallographical directions parallel to the olivine outlines. 
Figures 11 to 15 exhibit this secondary rutile. 




Fig. 11 





v\ 



FlG. 12 

Rutile in olivine 




The rutile needles have originated within from small 
particles of titanic iron enclosed in the olivine, or from 



THE MATUIX OE THE DIAMOND 



17 



titanic acid in its composition. Sometimes a grain of 
titanic iron can be seen imbedded in the rutile needles, as 
in fig. 10. The rutile crystals are rarely geniculated. 





Fid. 11. Rutile 



Fig. 15. Id. Fit;. 16.— (with titanic iron) 



The production of secondary rutile through the decom- 
position of olivine does not appear to have been previously 
noticed, although in decomposing phlogopite or biotite [ it is 
a not uncommon occurrence, and its association with 
titanic iron a is well known. One of the most interesting 
and unusual features of the olivine in this rock is that it is 
younger than or contemporaneous with the chrome diop- 
side and bronzite. Bronzite occurs enclosed within it, but 
olivine has not been observed enclosed within the bronzite. 
"When thus enclosed in the olivine the bronzite is of more 
or less rounded form. 

In fig. 17, a rounded grain of clear diopside with good 
cleavages or partings is enclosed in fresh olivine (Kentucky 
peridotite) . 



d 





Fig. 17.— Kentucky peridotite. d, diopaide 
o, olivine 



p I(i> is._r, enatatite, with specks 
of biotite 



1 Cohen, Nenes Jahrb. 1882, ii. p. 194. 

- Cathrein, Zeits.filr Kryst. vi. 1882, p. 244 ; Lasaulx, Zeits.filr Kryst. 

viii. 1884, p. 54. 

C 



18 THE MATRIX OF THE DIAMOND 

In fig. 18, the enclosed mineral is enstatite, distinguished 
from the diopside by much lower double refraction and by 
parallel extinction. The enstatite here encloses secondary 
biotite scales, and the biotite in turn contains small hexa- 
gons of hematite. 

As is well known, olivine is almost always older than 
the more acid pyroxene in any given rock. Unless we sup- 
pose that a subsequent fusion has produced it, or that there 
is a secondary olivine, there would appear to be an excep- 
tion here to the useful and generally applicable rule that the 
constituents of a magma crystallise out in the order of 
diminishing basicity. 1 According to Hussak, 2 augite and 
hornblende occur enclosed in olivine in the picrite-porphy- 
rite of Steierdorf, Banat, and the enclosure of enstatite in 
olivine is often seen in meteorites. It is probable that 
these are cases of contemporaneous crystallisation. 

A highly refracting rhombic mineral, resembling olivine, 
also occurs in some remarkable zones which surround the 
bronzite in the Kimberley rock, and which have the appear- 
ance of contact-fusion zones. These zones, in which the 
olivine makes a pegmatitic or ' eozoonal ' structure, as in 
the chondri of meteorites, will be discussed more fully under 
the description of enstatite. They may be the rudimentary 
stage of the compact olivine enclosing enstatite, and point 
to the contemporaneous and rapid crystallisation of olivine 
and enstatite — a common occurrence in meteorites. 

The significance of olivine as a characteristically igneous 
mineral, and as one readily produced by dry fusion, is well 
known. 3 It is a mineral of special interest, as regards the 
part it plays in connecting deep-seated terrestrial rocks with 
those of celestial origin, 4 As the predominating constitu- 
ent of the present rock, it places this clearly among the 



Kosenbusch, Neucs Jahrb. 1882, ii. p. 7. 

2 Verhandl. der geol. Reichsanstalt, 1881, p. 2G0. 

3 Bourgeois, Reproduction Artificielle des Mine'raux, Paris, 1834, p. 108. 

4 Daubree, Etudes Synthetiques de Gtologie ExpMmentale, Paris, 1879, 
533 ; Wadsworth, hithohxjical Studies, 1884, p. 84. 



THE MAT1UX OF THE DIAMOND 



19 



peridotites, while the idiomorphic character of the crystals, 

and the evidence of the action of a corrosive magma upon 
them, class the peridotite among the volcanic rather than 
the plutonic series. 

Pyroxenic Minerals. — Three clear green minerals, almost 
identical macroscopically, occur in the peridotite of Kimber- 
ley, and are found loose in the decomposed * blue ground. ' 
These are smaragdite, bronzite, and chrome diopside or dial- 
lage. These minerals are so hard and clear and free from 
inclusions that they have been cut as gems. They all have a 
light grass green colour, and are unattacked by acid, and 
all sink in a Thoulet's solution, having a specific gravity 
of 3. They can be distinguished from each other by specific 
gravity, by blowpipe tests, and especially by optical means. 
All are coloured by chrome oxide, as is shown by blowpipe 

tests. 

Smaragdite. — This has the hornblende cleavage, and an 
extinction of about 15°. It has a tine green colour, and in 
thin sections it is pleochroic in shades of green. The 
mineral has been analysed by Maskelyne and Flight, who 
found the composition of loose fragments in the blue ground 
of ])u Toits Pan to be as follows : 



SiO, . 

MA 
FeO 

CaO 

MgO 

Na,0 

11,6 . 



(with Cr 2 3 ) 



52-97 
1-94 
4-52 
20-47 
17-49 
1-77 
0-58 

99-74 



Bronzite and Bastite. — Of the three related green 
minerals in the peridotite, bronzite is the most abundant. 1 It 



1 In the specimens from Kimberley, examined by Miss Raisin and my- 
self (Oeol. Mag. 18 ( .)5, p. 496), the green mineral in most, if not in all.casas 
was not an enstatite, but an augite. — T. CI. J>. 

c 2 



20 



THE MATRIX OF THE DIAMOND 



occurs in crystals or crystalline plates with the characteristic 
fine striation of enstatite, parallel to the vertical axis. It 
has a weaker double refraction than the other two minerals, 
its colours in polarised light being of the first order. It 
gives parallel extinction, and the cleavage plates show no 
hyperbolas. The plane of the optical axes is parallel to the 
cleavage. The colour is a paler green than that of the 
other two minerals. Before the blowpipe it is infusible, or 
nearly so. The specific gravity, as determined in Klein's 
cadmium solution, was 3*199. Maskelyne and Flight ! have 
analysed loose fragments from the * blue ground/ of Du 
Toits Pan, as follows : — 



KK>* 



kJUV/ 2 . 


• • • 


• *J t J ij ± 


aia 


• • • 


2-64 


Cr 2 3 . 


* • • 


. 0-54 


FeO. 


• • • 


4-99 


NiO . 


• • • 


trace 


MgO 


• • • 


. 34-91 


CaO. 


• • • 


0-45 



99-44 



They draw attention to the resemblance of this bronzite 
to that in the meteorite of Breitenbach. If, with Tschermak, 2 
we draw the line between bronzite and enstatite at a con- 
tent of 5 per cent, of iron protoxide, it will be seen that 
our mineral is just on that line; and thus, as having an 
intermediate composition, may be called with equal pro- 
priety either bronzite or enstatite. 

The bronzite sometimes alters into biotite, which may 
occur in it in scales or plates which appear to be secondary. 
It also alters into bastite, which often entirely replaces the 
bronzite, and may be quite an abundant constituent. Bastite 
is distinguished from bronzite by a faint yellowish colour, 



1 Quart Jo?mi. Geol. Soc. xxx. 1874, p. 411. 
8 Lehrb. tier Mineralogie, Wien, 1885, p. 443. 



THE MAT BIX OF THE DIAMOND 21 

weak pleochroism, and by the appearance of a bisectrix in 
cleavage flakes. The plane of the optic axis is parallel to 
the fibres, and there is parallel extinction, it has a some- 
what more fibrous character than bronzite, and with the 
latter forms the most abundant constituent of the rock 

after olivine. 

The blue fibrous substance which forms an alteration 
rim around olivine has already been mentioned. This 
peculiar mineral, common in the Kentucky rock, has a 
dark indigo colour, and is faintly pleochroic, being dark 
indigo blue when the nicols are parallel to the fibres, and 
light greenish blue when at right angles (c > b or ). 
The plane of the optic axes is parallel to the fibres and the 
c axis and c = r. The blue colour disappears on heat- 
ing the slide in acid, and the mineral is gelatinised. All 
these are the characters of bastite. In some cases it is 
almost isotropic, while in other cases some of the fibres 
have a double refraction nearly as high as enslatite, the 
tints rising nearly to yellow of the first order. In colour it 
somewhat resembles glaucophane. 

Bastite is well known as an alteration product of bronzite, 
but has not previously been observed as a result of the 
change of olivine. From this circumstance, and from its 
deep blue colour, it may be justly considered as a new 
variety of bastite. 1 

Chrome-diopside. — The chrome-diopside has a fine 
emerald green colour, richer than that of the other two 
minerals. The specific gravity is higher than that of 
bronzite, being 8*267 (determined in cadmium solution). 
Its ready fusibility before the blowpipe, and its much higher 
colours in polarised light, also distinguish it from the 
bronzite. Cleavage fragments show a very faint pleochroism, 
not nearly as distinct as that of smaragdite, and an extinc- 



1 I have occasionally observed a blue tinge, almost like a stain, and 
generally similar to this, in examining dark-coloured serpentines. I doubt 
whether its value is so great as to constitute a variety.- T. G. 13. 



22 THE MAT BIX OF THE DIAMOND 

tion angle of 39°. In converging polarised light an axis 
appears on cleavage fragments which are parallel to qc Poo . 
Three cleavages or partings, each well developed, also 
occur in chrome-diopside, so that it readily cleaves into 
almost cubical rhombs. It has an excellent cleavage 
parallel with qo Pgo , another, less perfect, parallel with 
ooPcb, and another parallel with OP. This last is the 
salite parting, and not a true cleavage. It is probably, as 
Tschermak, 1 Vom Eath, 2 and others have shown, due 
to the interposition of thin twinning lamella) parallel 
to the base, and the mineral might be called a salite. 
Von Koksharow 3 speaks of the ' zusammensetzungflachen ' 
in chrome-diopside from the Urals as often confounded 
with true cleavage faces. The ordinary augitic prismatic 
cleavage is not apparent microscopically on these basal 
parting sections, but the pinacoidal cleavages are seen as 
fine lines crossing each other at right angles and parallel 
to the sides of the section. 

A cleavage fragment gave the angles oo Poo A P = 106° 
and oo Poo A OP = 90°. ' 

The face of the best cleavage, parallel to oo P3o has a 
pearly lustre, and is nearly or quite free from stria?. The 
orthopinacoidal cleavage plates are striated vertically, and 
show in convergent light a single axis identical with' that 
seen in cleavage plates of diallage. 

The low extinction angle, 39°, is typical of a pure lime- 
magnesia diopside, free from iron, for both iron and mag- 
nesia, as Tschermak, 4 Wiik, 6 Herwig * and Doelter'have 
shown, tend to increase the extinction angle. The so- 
called omphacite, occurring in eclogites, peridotites, olivine 
bombs, and serpentines, seems to be but another name for 

I *** ****• 1871 ' P' 22 ' - Zcits. fur Kryst. v. 1881, p. 495 

Mater lahen zur Mineralogie Busslands, iv. 1862, p 259 
4 Min. Mitth. 1871, p. 22. 

• Finska Vetensk. Soc. Forhandl. xxiv. 1882, p. 33 ; xxv. 1883, p. 109. 

Irooramme des G W nn. Saarbrlickcn, Nr. 416, 1884 
7 Neucs Jahrt. 1885, ii. p. 43, 



THE MATRIX OF THE DIAMOND 23 

chrome-diopside, the composition and optical characters 

being identical. 1 

Chrome-diopside gives birth to granular calcite, which 
always accompanies it when decomposed. When there is 
any doubt in the section as to whether a mineral is bronzite 
or chrome-diopside, the presence of calcite on its edges 
and in its cracks is often a sufficient criterion for diopside. 
The composition is probably that of the pure diopside 

molecule, CaO, MgO, 2Si0 2 . 

Chrome-diopside is well known to occur with enstatite 
in dunite, in lherzolite and in other peridotites and ser- 
pentines, and in the < olivine bombs ' which are enclosed 
in basalt. Descloiseaux has described a chrome-diopside 
in the platiniferous (and diamantiferous ? ) peridotite of 
Nischne-Tagilsk, Urals. 

Fluid or glass inclusions, resembling those in the olivine, 
were noticed in cleavage fragments of the chrome-diopside, 
which were otherwise pure. 

The fact has already been pointed out that bronzite and 
chrome-diopside occur sometimes enclosed in olivine, and 
sometimes surrounded by what seems to be a fusion zone. 
This fusion zone or growth zone has a peculiar worm- 
like radiating structure, which may be compared with 
that of the kelyphite rim' 2 around garnets in serpentine, or 
the radial zones around olivine in certain norites'* and 
gabbros, or the so-called granophyric 4 or pegmatitic 5 
structure in some quartz-porphyries, or the struc- 
ture in the chondri of meteorites/' The principal 
mineral in these zones is a colourless substance, in short 
worm-like forms, with a high index of refraction, high 



i Schrauf, Zcits.fiir Kryst. vi. 1882, p. 329, a Ibid. p. 358. 

» Tornebohm, Neuea Jahrb. 1*77, p. 383; Becke, Min. und Vetr. 
Mittli. iv. 1882, p. 450; Adams, American Naturalist, 1*85, p. 1087. 

* Rosenbusch, Mikrosk. Physiogr. ii. 1887, p. 388. 

* Michel Levy, Bull Soc. Giol France, iii. 1875, p. 199; Ann. des 

Mines, viii. 1875, p. 3*7. 

" Wadsworth, Lithological Studies, 1884, p. 89. 






24 THE MATRIX OF THE DIAMOND 

double refraction, positive character, parallel extinction, 
and with traces of vertical and basal clea\ age. The axis 
of greatest elasticity is at right angles to the best cleav- 
age (b= ). The high colours in polarised light are identi- 
cal with those of olivine, and serpentine sometimes replaces 
it. All these characters point to olivine as the mineral 
forming the greater part of the zone. These olivine prisms 
are all rounded, and radiate irregularly from the central 
bronzite. They are imbedded in a nearly amorphous 
glass-like brown serpentinous substance, and are accom- 
panied by small quantities of calcite, and of a mineral 
with a high index of refraction, but very low double refrac- 
tion, which occurs in rectangular prisms, has traces of a 
cleavage in partings parallel to the base, and is negative. 
This microlith, however, was noticed only in a few cases. 
Olivine, it seems, is the main constituent of these zones. 
The grains are generally so minute and crowded together 
that they form a grey highly refracting fibrous border or 
fringe around the enstatite, like leucoxene around titanic 
iron. Farther away from the enstatite the grains become 
larger and more worm-like, so that they can be separately 
studied. The structure of these zones resembles that figured 
by Becke, 1 as occurring around garnets in a garnet-olivine 
rock from Karlstatten, Lower Austria, and called by him 
'centric' structure. He has figured a similar structure 
in the omphacites of certain eclogites, a and speaks of it as 
' darmzottenahnlich.' 3 

It has often been called a pegmatitic or micro-pegma- 
titic structure, since, in many instances, a number of the 
grains have the same orientation, extinguishing simultane- 
ously, the two substances being contemporaneously crystal- 
lised. This is also the case, to a limited extent, in the 
zones under consideration. Perhaps the term centro- 
pegmatitic would more nearly express it. From its 



• Min. unci Petr. Mitth. iv. 1882, p. 326. (See Plate II. figs. 2 and 8 ) 



THE MATRIX OF THE DIAMOND 25 

resemblance to organic alga-like forms it might also bo 
called ' eozoonal.' More nearly allied, however, than any of 
these is a peculiar structure, often found in meteorites, 
for it is a phase of the so-called chondritic structure. As 
will subsequently appear, our rock has some close resem- 
blances, both in composition and structure, to certain 
meteorites ; the structure of the zone that we are now 
attempting to describe has frequently been observed in 
meteorites, and has given rise to various conjectures. 

In the Kentucky rock I have noticed the same peg- 
matitic olivine zones around the enstatite. The olivine 
grains in these zones are imbedded in a brown, nearly 
isotropic, substance, which suggests a serpentinised glass 

or base. 

Mica.— The mica is, next to the olivine, the most 
abundant mineral, and in hand specimens it is the most 
conspicuous mineral. When the rock has been exposed to 
the weather it appears sprinkled with glittering mica 
crystals which, when weathered, form silvery spangles on 
the black rock. The ' blue ground ' and the soil about the 
diamond diggings, both at Kimberley and on the Yaal 
river, contain many fragments of mica, which is thus re- 
garded as the principal indication of diamonds. In the 
rock which we are describing it is of a dark red-brown 
colour, like biotite or phlogopite, and is apparently quite 
fresh and undecomposed. Plates half a centimetre in 
diameter are very common, and sometimes pieces occur 
two centimetres in diameter. It is brittle when fresh. 
Before the blowpipe this mica melts quietly to a dark 
glass— sometimes slightly exfoliating. 

Under the microscope the mica is seen to be nearly 
pure and unaltered. It occurs usually in thick isolated 
plates or crystals, lying like the olivine porphyritically in 
the ground "mass. These are frequently polysynthetically 
twinned, according to the law so ably expounded by Tscher- 
mak. It is indicated by the different absorption in the 
alternate layers. The extinction angle between the two 



26 THE MAT BIX OF THE DIAMOND 

alternate stride is about 10°, showing an extinction for single 
lamellae of 5°. 

The mica seldom occurs in well bounded crystals, being 
more usually found in irregular plates. Sometimes the 
crystals are corroded, as if from a re-solution of the magma. 
Sometimes also a narrow rim of ' opacite ' surrounds the 
mica, this being particularly observable in such crystals as 
have been greatly corroded and rounded. This black rim 
(the'opaeit rand') is never thick, and is only sometimes 
present. Sometimes the edges of the mica crystals are 
curved, this being the result of motion in the rock. In 
certain cases the mica is found to contain very small 
short thick rods of a highly refracting dark red substance, 
probably rutile. These r utile needles lie parallel to the 
base, and are probably a result of the partial decomposition 
of the mica. They indicate that the mica contained a 
small percentage of titanium. The production of rutile as 
a secondary mineral has been frequently observed in mag- 
nesia-mica. 1 

Another mode in which the mica occurs is around the 
garnets in the rock. Sometimes a large red pyrope will be 
entirely surrounded by a narrow zone of brown mica. 

A third method of occurrence of the mica is in the form 
of small scales in enstatite, here apparently due to the 
alteration or corrosion of that mineral. This was noticed 
in only a few instances, and especially in those in which the 
enstatite was enclosed in olivine. In one instance, small 
scales of magnesia mica alone were enclosed in olivine/ as 
though the original enstatite had been entirely replaced 
by the mica. 

A fourth association in which we find magnesia-mica 
is as a product of the apparent fusion or metamorphism of 



RoBenbusoh, Ml krosk. Physiogr. i. 1885, p. 483 ; Dathe, Zeits. Deutsch 
^olGcscll xxxiv. 1882, p. 35; Cross, Min. und Petr. Mitth. iii. 1881, 
p. 372; Zirkel, her. der Sachs. Gcscll. der Wiss. 1875, p. 202; Kalkowsky 

£lS^^ ^ »« Willis, Ne Zi 



THE MATRIX OF THE DIAMOND 



27 



enclosed fragments of shale or other rocks. These enclosures 
are sometimes entirely altered into a nearly opaque dirty 
grey aggregate, largely composed of a pleochroic mica, ap- 
parently an impure scaly biotite. These mica scales are 
highly pleochroic, and are, perhaps, another mica than 
that which composes the large porphyritic crystals, for the 
latter seem to be primary constituents of the rock. By 
decomposition or serpentinisation the mica is altered into an 
irregular mass of sericite, or talc-scales, in which round or 
oval masses of an apparently isotropic gum-like substance 

occur. 

The optical characters of the mica are unusual. Un- 
like ordinary biotite, it has a weak pleochroism. As a 
prismatic section is revolved over the polariser the light 
brown colour, while varying in intensity, does not become 
dark. Similar weakly pleochroic magnesia-micas have been 
observed in other ultra-basic rocks. Zirkei l noticed such 
a mica in the leucitite of the Leucite hills, Wyoming 
territory ; and Judd * 2 has described an altered magnesian 
mica with feeble pleochroism in the ' Bcyelite ' of Caith- 
ness. 3 The mica in the Kimberley rock has the usual 
index of refraction and high double refraction ; it has a 
very small optic axial angle, and is a mica of the second 
order. The ' strike figure ' has one ray parallel to the 
symmetry plane, and to the plane of the optic axes. Opti- 
cally, therefore, it is a meroxene or phlogopite. 

Maskelyne and Flight l have analysed this mica in a 
decomposed state. In the soft ' blue ground ' of Du Toits 
Pan this mica in decomposing has absorbed much water 
and become a vermiculite, exfoliating when heated. To 
this substance Maskelyne and Flight have given the 



1 « Microscop. Petrogr.' U.S. Oral. Expl. 40th Par. vi. 1876, p. 261. 

2 Quart. Journ. Ocol. SV>c. xli. 1885, p. 105. 

3 [I have observed a rather similar mica in a picrite from Sark, which 
presents a considerable resemblance to scyelite. Oeol. Mag, vi. 1881), p. 110. 
- T. Q. B. 1 

4 Quart. Journ. Gcol. Soc. xxx. 1871, p. -iO'.K 



28 THE MAT BIX OF THE DIAMOND 

name of ' Vaalite.' In this state it is a soft yellow or bluish- 
green micaceous mineral, containing nearly 10 per cent, of 
water. 

The following is the composition of the ' Vaalite ' : — 

Si0 2 40-83 

A1 2 3 9*80 

Fe 2 a 6-84 

Cr 2 O a . trace 

MgO 31-34 

Na 2 . . . . . 0-67 

H 2 9-72 

99-20 

Garnet — Deep-reel rounded grains of clear pyrope are 
abundant in the ' blue ground,' and these, with black grains 
of titanic iron, remain with the diamonds in the final wash- 
ings. Pyropes are also seen imbedded in the dark green 
peridotite rock. They have been utilised as gems. The 
pyropes which were observed in thin sections were isotropic, 
nearly pure and always rounded. In one case a pyrope 
was surrounded by a zone of magnesia-mica. Cracks 
penetrate the pyropes irregularly, as is usual. 

Another variety of garnet occurs, which greatly resem- 
bles the diamond. These garnets are very small, colourless, 
or with a faint tinge of green, and have such a high index 
of refraction that it is difficult to see their shape. They are 
crystallised apparently in forms strongly suggesting the dia- 
mond, the faces being sometimes curved, and the octahedral 
forms apparently predominating. They are unattacked by 
acids, including hydrofluoric acid. They melt readily to 
glass in a crucible, and may thus be distinguished from dia- 
monds. Most of them are so small as to be seen only with 
high powers, and they are then readily confounded with 
minute diamonds. They probably belong to the variety of 
garnet called ■ demantoid,'. 1 which is found in the diamond 



1 Kammelsberg, ZciU. Deutsch. GcuL Gcscll. xxix. 1877, p. 819. 



THE MATRIX OF THE DIAMOND 



29 



region of Syssersk, Urals, imbedded in serpentine. 1 Other 
small garnets, again, of bluish-green colour, giving a chrome 
reaction, may belong to the variety named ' ouvarovite.' 

The pyropes are about as abundant as in the garnet- 
bearing serpentines, and it is probable that many of these 
serpentines have been derived from a peridotite of similar 
nature to that now under consideration. These serpentines 
are related not merely in the occurrence of garnet, but also 
in the association of olivine, bronzite, diallage and some- 
times perovskite, and even diamond. 

Perovskite. — Perovskite is an abundant and charac- 
teristic mineral in the rock under consideration. It occurs 
in crystals, in crystalline aggre- 
gates, and in combination with 
ilmenite. It was isolated with the 
garnets from the other constituents 
by treatment with sulphuric and 
hydrofluoric acids, and submitted 
to blowpipe tests. Most of the 
mineral thus isolated was in the 
form of brownish-black cubical crys- 
tals, with octahedral truncations 

(fig. 19). These crystals were almost all of a nearly uniform 
size. In the thin sections the perovskite appeared as reddish- 
brown crystals or aggregates, deep yellow when thin, but 
sometimes nearly opaque, scattered abundantly through 
the ground-mass. In their deep colour and very high index 
of refraction they resembled the rutile grains of the 
crystalline schists, but were readily distinguished from that 
mineral or from zircon by their remarkably low power of 
double refraction. The colour in polarised light seldom 
rose above grey of the first order, and was sometimes as 
high as white of the first order. The characteristic optical 
properties therefore are an index of refraction nearly as 




Fir;. 19.— Ferov<'kite 



1 Losch, Neues Jahrb. 1S7<), p. 785 ; Verhandl. der Buss. Miner. Getell 
xiii. 1978, p. 432 ; xvi. 1881, p. 2D ( J. 



80 



THE MAT BIX OF THE DIAMOND 



. 



high as rutile (over 2) and a power of double refraction 
about as low as zoisite (y — a = -005 ). The low double 
refraction, together with the opacity often caused by in- 
clusions of ilmenite or chromite, might in some cases cause 
it to be mistaken for a dark spinel or other isotropic 
mineral. In no case, however, is the perovskite isotropic. 
Extinction always occurs parallel to the diagonal of the 
cube. Pleochroism is extremely faint. The form and 
optical properties of the- perovskite show that in all cases it 
belongs to the rhombic system, and is in the form of twins, 
or of aggregates of twins. The commonest form is that 
of interpenetrative twins, so crossed as to form a cube. 
The following are common forms as seen in ordinary 
light : — 







Fig 20 




O 




O 



— # -— 



Fkj. 21 



Fig. 22 Fig. 23 

Figs. 20-23.— Twinned perovskite 



A cleavage or parting occurs parallel to the cubic faces. 
Re-entrant angles usually divide the elements of the twins, 
but these are still better indicated by the optical characters 
of the mineral. The extinction is always parallel to the 
diagonal of the cube, as shown by the dotted lines in 
figs. 21, 22, and 23. The apparent cube appears to be 
composed of interpenetrating rhombic individuals, whose 



THE MATRIX OF THE DIAMOND 



31 



basal pinacoids form the octahedral replacements of the 
cube. Very frequently four individuals are seen grouped 
to form a single square, dark lines dividing the deep yellow 
crystal. The entire cube would then be composed of six 
individuals. 1 

A second kind of twinning is also common in this 
perovskite, producing the appearance with crossing nicols 
of a series of parallel alternately coloured bands, like the 
polysynthetic twinning in plagioclase felspars. The bands 
are again often crossed at right angles, as in microcline. 
These lamellae are parallel to the cubic faces of the com- 
pound twin. They are alternately pale greenish-blue and 
pale greenish-yellow, and are all simultaneously extin- 
guished when they are turned at an angle of 45° to the 
nicols. The following are among the forms which are seen 
by the use of this apparatus : — 






£ 





■ II 


\ 


J 


X 





Fig. 24. -Twinned perovskite (crossing nicols) 



It seems, therefore, that a series of rhombic prisms are 
twinned according to two laws at the same time, the 
apparent cubo-octahedrons being in reality compound 



i u 



See Neucs JaJirb. 1878, p, 38. 



32 



THE MAT BIX OF THE DIAMOND 



twins. The following, fig. 25, represents diagrammatieally 
this double twinning. 

op? 




Fig. 25. — Twinned perovskite 

We have here apparently a polysynthetic or parallel 
growth, and a simple interpenetrative twinning according 
to P. The optical peculiarities of perovskite have long been 
a subject of discussion, and diverse views are at the present 
time held as to the crystalline system to which it belongs. 
Borne crystallographers * hold that perovskite is a regular 
mineral, with optical anomalies which are due to strain ; 
while others 2 believe it to be a rhombic mineral, occurring 
in compound twins belonging to the class of ' mimetic ' 
minerals. 

The brighter colours of single lamella}, and of certain 
portions of the compound crystals \x\ the Kimberley rock, 
suggest that the very weak double refraction exhibited by 
the crystals, as a whole, may be due to the overlapping of 
two or more simple components producing a compensation ; 
a weak double refraction belonging to the untwinned 
mineral. The re-entrant angles, so common in the 
Kimberley crystals, seem to have been rarely observed 



1 Klein, Zirkel, Ben Saude. 

2 Descloiseaux, liaumhauer, Groth, Von Koksharow, Tgchermak, Ac. 



THE MATBIX OF THE DIAMOND 



33 



in the perovskites of other localities. The striation 
parallel to the cubical faces, extinguishing when the section 
is at 45" to the polar isers, occurs also on perovskite from 
Zermatt, from the Urals (where also all the crystals are 
penetration-twins), from the Tyrol, from Arkansas, from 
Wiesenthal (Erzgebirge), &c. The figures of perovskite 
grains out of the nepheline-basalt of the last locality, as 
given by Saner, 1 are very similar to those given above from 
the Kimberley mineral. 

Perovskite also occurs in the Kimberley peridotite in 
aggregates of crystals and in irregular grains. Very fre- 
quently these crystals or grains enclose one or more opaque 
black octahedral crystals of a titaniferous magnetite (or 
other spinellid). Often an octahedron or cube of perovskite 
will have a black grain in the very centre, and when an 
aggregate of such crystals occurs, each of its components 
may have a black grain in its centre. 



^ 





"Km;. 2(i. 'Inclusions in perovskite 



Fig, 27. Titanic iron in perovskite 



This is so common an appearance that one is led to 
suspect that the perovskite is a secondary mineral, made 
out of the older titanic iron through some reaction with the 
basic magma. While, generally, the titanic iron is in the 
form of small grains in the perovskite, as shown in the 
above figures, sometimes the perovskite forms a narrow 
fringe on one side of a larger mass of titanic iron, or makes 
a shell around it. Sometimes also a crack in a mass of 
titanic iron is filled with perovskite, as if by a secondary 
mineral. 

That titanic iron is older than the perovskite is proved 
by the fact that while titanic iron occurs as an enclosure 
in the olivine, perovskite never does so. 



Zt'its. Deuiscli. Gcol. Qesell. xxxvii. 1885, p. 417. 



L> 



u 



THE MATBIX OF THE DIAMOND 



It is very common to find the small perovskite crystals 
surrounding a large crystal of olivine, as if attracted to it. 
The following figures are examples of this peculiarity :— 



f 





Fie.. 28.— Perovskite surrounding 

olivine 



r — 



Fie 29.— o, olivine : r, rutile ; 
»-, serpentine; p t perovskite 



The perovskite crystals lie on the outer sides of the 
olivine crystal, as if a later growth. In the same 
manner perovskite is attached to the outer surface of 
serpentine pseudomorphs after olivine. Fig. 29 shows 
such a case, and shows also in the serpentinised olivine 
secondary rutile needles growing out of a grain of titanic 
iron, as already descrihed under olivine. 

A similar grouping of small perovskite crystals, like a 
wreath, around the olivines ias been noticed by Stelzner 1 
in the melilite-basalt of Hammerer Spitzberg, near Warten- 
berg, Bohemia (the so-called 'nephelin-pikrit' of Boficky), 2 
which is rich in perovskite. 

Perovskite is one of the most characteristic minerals for 
the felspar-free basic eruptive rocks. As a rock ingredient 
it was first detected by Boficky 3 in the above-named 
melilite-basalt of Wartenberg. Hussak 4 proved its exist- 
ence in the nepheline and leucite lavas of the Eifel ; 
Stelzner 5 showed that it was a constant constituent of 
melilite-basalts, and Sauer fl that it occurred very commonly 
in the nepheline and leucite-basalts of the Erzoebiroe 



1 Neues Jahrb. Beil. Bd. ii. 1883, p. 415. 

2 Sitzber. der math.-naturw. Classe der bohm. Gesell. Prague 1876 
P- 229. 3 LoCt ciL 

4 Sitzber. Akad. Wicn, lxxvii. 1878 (Abth. 1), p. 841. 
■ Neues Jahrb. Beil. Bd. ii. 1883, p. 396. 

6 Erlauterungen zur geologischen Specialkarte des Kimigreiclis Sachsen. 
Section Kupferberg. Leipzig, 1882, p. 70. 



THE MATRIX OF THE DIAMOND 85 

Perovskite has not been identified in a peridotite until 
quite recently, when my friend, Dr. G. II. Williams, observed 
it in an eruptive peridotite closely resembling the Kim- 

berley rock — in the State of New York. It has probably 
been mistaken frequently for other minerals. The 
colour and form, the similarity to picotite, the included 
opaque grains, and the mineral associations, all indicate 
perovskite rather than zircon. Diller 1 has described, as 
probably anatase, certain yellowish, highly-refracting grains 
occurring around and penetrating ilmenite in an eruptive 
porphyritic peridotite in Elliott County, Kentucky. Through 
the courtesy of Mr. Diller and of Prof. A. R. Crandall, I 
have received specimens of this interesting rock, and find 
that these grains are identical with the perovskite of the 
Kimberley rock.- The same form, colour, and enclosures, 
the same twinning structure, the same high index of re- 
fraction and low power of double refraction, and the same 
mineral associations, occur in the Kentucky as in the Kim- 
berley peridotite. 

It is an interesting fact that, speaking generally, the 
titanium in acid eruptive rocks takes the form of sphene, 
in basic non-felspathic rocks of perovskite, and in rocks of 
intermediate basicity, the felspar-basalts, of ilmenite or 
titanic iron. An explanation is offered by an important 
experiment performed by Bourgeois, 3 who was able to form 
artificial perovskite by fusing its elements with various 
silicates and basic rocks, and who found that below a certain 
point of acidity only perovskite was formed, while above 
that point only sphene was produced. With a titanic 
spinellid as the primary titanium mineral, the reaction of 
a basic magma would produce perovskite (as in leucite- 
and melihte-basalts and in peridotite), while the reaction 
of an acid magma would produce sphene (as in granite, 



1 Amer. Journ. Sci. xxxii. 1886, p. 124. Mr. Diller has since withdrawn 
this opinion.] 

'-' For a description of this rock see Section ILL 
3 Ann, Phys. Chun. xxix. 1883, p. 481. 

d 2 



86 



THE MATRIX OF THE DIAMOND 



and trachyte). 1 In both cases the titanic spinellid or 
ilmenite is surrounded or penetrated by the younger sphene 
or perovskite, silica being necessary for the formation of 
sphene out of titanic iron, but not for that of the more basic 
perovskite. 



ii 



o 





Fig. 30.— Perovskite. I, plain ; II, polarised 

The other minerals, which are to be found in examining 
the specimens from Kimberley, with the exception of the 
diamond, are less important. 

Magnetite, chromite, titaniferous-magnetite, and picotite. 
— four isomorphous minerals with difficulty distinguished 
from one another 2 — occur in small grains or crystals scattered 
through the ground-mass. Chromite is, perhaps, the most 
abundant of the four, and is primary, while magnetite may 
in part result from the decomposition of the olivine. The 
chromite is abundant in minute octahedrons. It is a 
mineral to be expected in a magnesian rock, occurring in 
almost all serpentines. Picotite or pleonaste occurs in similar 
minute grains, the latter of a dark green colour in trans- 
mitted light. Both the chromite and the spinel-mineral are 
much smaller than the perovskite crystals. 

Another black mineral in octahedrons occurs in asso- 
ciation with rutile. Ilmenite proper is, of course, rhom- 
bohedral, and usually is in thin plates. This mineral may 
be the same that so often occurs in basalts, and was called 
' trapp-eisenerz ' by Breithaupt. In titaniferous magnetite 

1 Sphene also occurs in cltuolite-syenite and phonolite. 
8 For some remarks on this point see Wadsworth, Lithological Studies, 
section vii. 



THE MATRIX OF THE DIAMOND 



37 



of this character, in the nepheline-dolerite of Meiches, Knop l 

found 25 per cent, of titanic iron. 

llmenile is in plates with a purplish metallic glance, as 
in Rowley Regis basalt ; and also probably in grains. 

Apatite.— In small hexagonal colourless crystals, with a 
high index of refraction and a low double refraction. The 
crystals are unusually short, and have a negative character. 
Sometimes the apatite is faintly pleochroic. It occurs in short 
crystals in the ground-mass, and also in long actinolite-like 
crystals, apparently as a contact mineral around enclosures. 
Epidote is in pale yellow grains, with a high index of 
refraction and a weak yellow pleochroism, and is apparently 
a secondary mineral due to decomposition. 

Orthite is one of the most interesting of the non-essen- 
tial minerals. It was noticed in large rounded cleavable 
grains, as if a primary constituent. It has a chestnut- 
brown to yellowish-brown colour in transmitted light, and 
is pleochroic. The pleochroism is more marked than that 
of epidote, changing from light to dark brown. It has a 
very high index of refraction, so that its surface appears 
wrinkled or shagreened. The double refraction is not so 
high as that of olivine. It has an excellent cleavage parallel 
to the base, OP, and another parallel to ooPoo. On the 
basal face or cleavage plane an axis appears in converging 
light not quite in the centre of the field, and this axis 
shows a hyperbola coloured green inside and red out- 
side, as in epidote. 2 The plane of the optic axis is diagonal 
to the cleavage, and the character is negative. All these 
characters agree with those of orthite, although tins is a 
new association for that mineral. Orthite occurs in many 
granitic and hornblendic rocks, as shown by Tornebohm, 8 
Sjogren, 1 and others, and was found by Vom Hath 5 in 



1 Nettea. Jahrb. 1877, p. 696. 

8 llosenbnsch, Mikrosk. Physiogr. i. 1885, p. 496. 

" Vega-Exped. Vetensk. Iakttagelser, Stockholm, iv. 1887, p. 124. 

' Stockholm, Qeoh Form. FVrhandL uu 1876 77, p. 2-38, 

1 Zcits. Deutsch. Geol Gescll xvi. 1864, p. 255, 



38 THE MATltlX OF THE DIAMOND 

tonalite, biit seems not to have been previously observed in 
peridotite or serpentine. 

Tourmaline, in strongly pleocbroie short prisms, is a 
rare but interesting constituent of the rock, being especially 
abundant arouudcertain inclusionsof shale. 1 Itspleochroisiii 
changes from brown to light blue. This and other minerals 
in small quantities are best detected after treating the tbin 
section with hydrochloric acid. 

Spliene, or titanite, was rarely observed, only a few 
irregular grains being noticed. The iinely fibrous form of 
sphene as a secondary mineral, known as leucoxene, also 
rarely occurs. 

Tremolite lias already been described, also rutile, as 
secondary minerals. 

Serpentine and serpentinous minerals, as already stated 
form a large part of the rock, resulting from the decom- 
position of olivine. 

Tak.—Yery minute scales of this mineral were noticed 
in the ground-mass, and, as a contact or alteration mineral 
around certain enclosures. It was highly refracting, had a 
wavy sheen, high colour, and parallel extinction. 

Caleite is abundantly present in this rock. Diopside 
can be seen directly altering into this mineral, but the 
quantity of diopside is so small that we must look else- 
where for the large mass of caleite that penetrates the 
rock. It is possible that some readily decomposed lime- 
bearing mineral, like melilite, originally furnished it; but it 
may be that, as Cohen 2 has suggested, the lime has filtered 
in from without. Caleite is said frequently to form a crust 
around the diamonds. 



f J.V 11 ' bc , lememb01cd that tourmaline is very often a product of eon 
tact metamorphism in an aluminous rock.- T G B 

in lr N 'T J 1' rb ,\ Bei1 ' !*' V> 18 * 7 ' P - 196 " °° hen hcl '° ho,fls - i" opposition 
to Moule and others, that the -calc-tuff- encrusting the 'blue "round" 

at the d.amond mine* is not derived from the diamantiferous ground but 
Peri d P ° Slt r ° ffi bl ' aCkiBh WatW dUline a de P re88ion tothePleiBtocene 



THE MAT HI X OF THE DIAMOND 



39 



Zeolites occur in cavities and cracks as a product of 
infiltration and decomposition. They are very rare in the 
hard rock here described, but nearer the surface of the 
mine they occur abundantly in the decomposed blue ground, 
sometimes forming rock like masses. The principal zeolite 
is natrolite. Fibres of natrolite were seen in thin sections 
radiating inwards, with a more or less tufted arrangement, 
from the outer edge of a mass of calcite. 

Chalcedony was observed in one instance filling a 
microscopic cavity in the rock. 

Cyanite.—A microscopic mineral .occurs in minute 
quantity in the peridotite, whose exact nature is uncertain, 
but whose optical characters seem to agree more closely 
with cyanite than with any other known mineral. It is 
particularly interesting, as forming usually a zone around 
enclosures of shale and other rocks, as if a contact mineral. 
It usually forms a fine compact crystalline zone, but some- 
times the separate crystals are large enough to be 
separately studied under the microscope. It occurs in 
fibrous masses resembling cyanite or actinolite, and has 
the following properties : a high index of refraction, about 
equal to that of pyroxene ; the double refraction low, 'being 
lower than in actinolite. It is very faintly pleochroic from 
pale blue to faint green, or, more accurately, pale lavender 
(corresponding to a) to pale greenish-lavender (correspond- 
ing to C). The fibrous structure is well marked m this 
mineral- It has two cleavages, one parallel to the fibres, 
and one at right angles to them, the latter 
often causing a separation, as in apatite. 
The crystals seem to be brittle, being 
often broken, as is so common in silli- 
manite. It has a large angle of extinction 
( = 32°— B5°). It is unattacked by acid. 
All these characters seem to be those of 
cyanite. It would be curious, however, 
to find cyanite forming contact zones around enclosures 

in a peridotite. 



& 



->c 



U 




I'm. 31.- Cyanite? 
a, lavender; c, greenish 



40 THE MATRIX OS THE DIAMOND 

Diamond.— We have deferred to the last the considera- 
tion of the most interesting mineral in our rock. While 
the diamond is very difficult to observe in thin sections, it 
has been found abundantly in the decomposed portion 
of the peridotite. In practice it is obtained by the fol- 
lowing process ' : The < blue ground ' is spread out upon 
the ground and exposed to the sunshine. After a period, 
dependent on the original condition of the rock, it has 
crumbled to a coarse powder, and is then placed in rotating 
washers, and all the lighter material washed away. The 
residue of chromic and titanic iron, garnet, pyroxene, &c, 
among which are the diamonds, is then picked over by 
hand, and the diamonds are separated. The number of 
diamonds thus obtained is something extraordinary. It is 
interesting also to find that they become more abundant 
the deeper they are from the surface, and where also the 
volcanic action was more intense. They are well crystal- 
lised in sharp octahedrons, also in dodecahedrons, at times. 
The crystallography of African diamonds 2 has been de- 
scribed by several mineralogists, and it is not to our 
purpose to enter upon that subject. 

Carbonados and black diamonds are also common not 
only in large crystals, but very abundantly as minute 
almost microscopic, crystals. The abundance of these 
minute crystals is another proof that fhey are not 
enclosures brought up from some other matrix. 

I feel some hesitation in describing certain small highly 
refracting crystals in the thin sections of the rock which 
may possibly be referred to as diamonds. Former at- 
tempts to describe microscopic diamonds in rock sections 
haye not been successful. Thus, Professor Jeremejew' 

m 'n T ' E ^ nert ' CalK ° f Gcod H °P e # eial Handbook, 1886, p. 218 

ue i Ainque clu bud, Ann. des Mines, vii. 1885 p l<m 

1886 A p m 250. latel ' PaPelS ai ' e KUBZ ' PWC - AnU ' r - Acad - ScL and **, xxxiv. 

BeL Suvl Dia v ante i"f h '"f eim X * n *0PhyUHder Schi.chim.kiwh*, 

•oeige oes Uials, JSeues Jahrb. 1871, p. 589. 



THE MATRIX OF THE DIAMOND 



11 



thought he had found microscopic diamonds in xanthophyl- 
lite From the Urals, the diamonds, in the form of hexa- 
kistetrahedrons, being held to be very abundant ; but 
Professor Knop, 1 after a very painstaking and convincing 
examination, proved the supposed diamonds to be merely 
holes in the xanthophyllite, the holes being probably 
negative crystals due to corrosion. By rubbing copper 
oxide on a dry slide he Idled these holes with the black 

powder. . 

Another supposed discovery of diamonds in the matrix 

was announced by Fouque and Levy, 2 in 1879. They 
thought that they had observed numerous small diamonds 
in a thin section of the diabase, the so-called ' ophite 
andesitique,' which forms overflow sheets in the Karoo 
shales, and they published photographs of these supposed 
diamonds in sections. But, as they afterwards found, 3 
these also were only holes. _ 

The very minute, isotropic, highly refracting crystals 
occasionally seen in a thin section of the Kimberley 
peridotite are certainly not holes, tor they are sometimes 
of a faint yellowish, or, more frequently, bluish colour, and 
are often ' entirely embedded in the ground-mass. They 
never occur as enclosures in other minerals, but, like 
the perovskite, lie scattered in the ground-mass only; 
belonging, therefore, to a later 



ii 



in 



C A 

Fig. 32. — Minute diamonds 



generation of minerals than 

the olivine and bronzite. 

They are always in the form 

of entire crystals, even in 

the thinnest slide, as if they were too hard to be cut. The 

shape is that of an octahedron with rounded faces ; tn- 



• 'Ueber die Bedcutun- dor fur Diamant gehaltenen Einschlur.se im 
Xanthophyllit tier Sohischimskischen Berge des Urals,' Nates Jahrb. 1*72, 

p. 785. l ,. . 

- « Note sur lea Roches accompagnant et contenant le diamant dans 

l'Afrique Australe,' Bull Soc. Min. de France, ii. 1879, p. 21(3. 
3 Neues Jahrb. i. 1881, p, 194, 



42 



THE MATRIX OF THE DIAMOND 



angular facets are also seen. (In some cases larger holes of 
the same octahedral shape may be observed in the section, 
as though a crystal had dropped out during the process of 
grinding.) Frequently these bodies seem to have concave 
faces, viz., as in fig. 82, ii. and hi. ; this, however, is probably 
only an optical illusion. They sometimes have a decided 
yellow colour. They have a high index of refraction, and a 
dark rim around them. They are usually isotropic, but 
traces of weak double refraction in the centre of one of the 
crystals have been seen, a pale bluish colour appearing in 
certain positions, as if it were a crystal under strain. I 

took some of the same rock from 
which the section was made, and 
after pulverizing it, separated 
the heaviest portion by means 
of Thoulet's solution. This was 
put upon a glass plate with a few 
drops of water, and then rubbed 
with a polished sapphire. The 
sapphire wr.s clearly scratched. 
A photograph of one of these 
bodies (fig. 88) was taken by a 
friend, the supposed diamond 
lying between three crystals of titanic iron. Four of these 

supposed diamonds were seen in a single section of the 
rock. 

I am not, however, prepared to state that these bodies 
are diamonds, not having been able to isolate them. 
Several colourless isotropic minerals appear in the rock 
among which a colourless garnet, probably denftntoid 
occurs in small crystals and might readily be supposed to 
be a diamond. 

Mr. Hedley, of the Colonial Exhibition, from whom I 
obtained my specimens, informed me that diamonds have 
been found in the rock as well as in the soft decomposed 
material; but as yet their detection under the microscope 
cannot be said to be free from doubt. 




Fir,. 33.— Microscopic section of the 
Kimberley peridotite. ?, ilmenite ; 
t, titanic iron ; d, diamond (V ) 



THE MATBIX OF THE DIAMOND 



43 



The larger diamonds from Kimberley have been the 
subject of study by several investigators. They have been 
found sometimes to have optical anomalies due to strain, 
so that they are not perfectly isotropic. Fizeau thought 
this strain to have been caused by the unequal distribution 
of heat during rapid cooling; but Jannettaz 1 holds that 
the strain is due to compressed gas in the interior of the 
crystal. The latter theory seems to be supported by the 
fact that the diamonds frequently crack or fly to pieces 
after having been taken from the mine. It is a pheno- 
menon perhaps similar to that which occurs with the 
smoky quartz of Branchville, Connecticut, which, as 
Wright 2 has proved, is filled with liquid carbonic acid, and 
llies°to pieces with a report when struck, as so well 
described by Hawes. 3 The fact that fragments of the 
diamonds are often found separated in the mine has been 
Ufeed as an argument that the blue ground is not a volcanic 
rock but an aqueous mud derived from one. This argu- 
ment falls to the ground on our knowing that the separation 
of these fragments is not due to a tlow of the matrix, but to 
the bursting of the diamonds themselves on exposure to 

the atmosphere. 

The Kimberley diamonds contain various enclosures,' 
among which hematite is the most abundant. Zirkel,* 
before" the discovery of the South African diamond mines, 
gave a full resume of the inclusions in diamonds. Schrauf 6 
has described a curious case of one diamond enclosed in 
another, a fact formerly mentioned by Kenngott, 7 The 
researches of Harting 8 upon inclusions in diamonds, as 

" «Sur les colorations du diamant clans la lumia-e polarisee,' Bull. Sac. 
Min. de France, ii. ls7 ( .), p. 124. 

* Amer. Joiirn. Sci, xxi. 1881, p. 209, 3 ^id. p. 203. 

1 Cohen, Neties Jahrb. 1876, p. 752. 

» Zirkel, Mikrosk. Beschaff. der Min. L873, p. 250 (gives literature). 

■ Tschermak, Min. Mitth. 1873, p. 289. 

' Wien. Akad. Sitzber. x. L853, p. 182. 

» Verhdl. d> Kon\ ImtiU van Wetensch., Letterkunde dc, tc Amsterdam, 

vi. 1858. 



44 THE MAT BIX OF THE DIAMOND 

well as those of Brewster, Petzhold, Wohler and Desclois- 
eaux, Sorby and Butler, Damour and Dumas can only 
here be mentioned. The supposed discovery by Goepperfc x 
of plants and organic cells in the diamond has not yet been 
verified. 

The explorations of the last few years have placed it 
beyond question that the serpentine rock called 'blue 
ground' is in reality the matrix of the diamond. For a 
time it was thought that the diamonds were washed into 
the 'kopjes' from above, being mere alluvial deposits, as 
held by Mr. Cooper 2 and others ; afterwards, and until the 
present time, the idea has been general that they were 
carried up from below along with other inclusions, and 
that their true matrix was some gneiss or itacolumite far 
below, from which they had become detached by volcanic 
agency. Others again, such as Doll, 3 hold that while the 
serpeniinous rock is the matrix of the diamond, the latter is 
a secondary mineral due to the decomposition of the rock. 

But recent investigations seem to place it beyond ques- 
tion that diamonds are as much a part of the Kimberley 
rock as biotite, garnet, titanic and chromic iron and perovs- 
kite, and that, like these minerals, they may be considered as 
a rock ingredient. The fact that they continue just as abun- 
dant, if not more 30, the deeper the mines are explored : 
that they are never found in, or especially associated with, 
the foreign inclusions of gneiss, granite, or sandstone : that 
they are distributed abundantly through all parts of the 
rock : and that in each of the four principal mines the 
diamonds have distinctive features of colour, lustre, and 
shape, are, with the microscopical evidence of the eruptive 



1 'Ueber algenartige Einschliisse in Diamanten,' Brcslau. AbhandL der 
schlcs. Gcsell. filr vatcrlcuidische Cultur, Abth. for Naturwissenschaf'ten 
und Medioin, 1868-09, p. 61. He describes supposed alga) enclosed in 
diamonds, comparing them with Eozoon and Oldhamia. and names them 
1 Protococous adamantinus ' and ■ Palmogloeitea adamantinus.' 

2 Cooper, Proc. GeoL Assoc, hi. 1874, p. 331). 

3 Verhandl. geol. Reichsanstalt, 1880, p. 78. 






THE MAT MX OF THE DIAMOND 



45 



character of the rock, strong reasons for holding that the 
diamonds now lie in their original matrix. 

Ground-mass— All the above-described minerals lie, 
some of them porphyritically, in a ground-mass or base, 
which we may now examine. This is a more or less 
homogeneous serpentinous mass, which, by reason of the 
decomposition it has suffered, is very difficult to study. 
It is now mainly composed of a nearly isotropic serpentinous 
mineral mixed with calcite. By treating the slide with hot 
hydrochloric acid, the iron and calcite are dissolved away 
and the amorphous and more readily soluble portions of 
the ground-mass eliminated, so that traces of the original 
structure for the first time become visible. Forms of small 
prismatic crystals (possibly a pyroxenic mineral) can now 
be seen occasionally, and between them are traces of an 
isotropic substance which may indicate a non-crystalline 
base. Certain resemblances can be traced to the ground- 
mass of sundry decomposed basaltic or other basal rocks. 
The base now, however, is a greenish serpentinous substance 
full of calcite grains, flour-like grains of gibbsite, rounded 
dusty masses of ferruginous and kaolinic material, &c, the 
original structure being entirely lost through disintegration. 
Until fresher specimens are obtained it is impossible to speak 
with any confidence concerning the original structure of the 
ground-mass. In one case already mentioned, a brown glass 
was noticed enclosed in olivine. Any similar basic glass in 
the ground-mass has long since been entirely decomposed. 
Fragmented Enclosures.— Fragments, both of the adjoin- 
ing shale and diabase, and also of more deeply seated 
granite, gneiss, eclogite and other rocks, occur in the 
Kimberley peridotite. Those of shale are by far the most 
numerous, sometimes becoming so abundant as to form 
the greater portion of the rock. 1 A breccia of shale 



1 Nevertheless in a large specimen, given to m$ by Sir J. B. Stone, I 
could not with certainty identify any shale, even under thu. microscope, hut 
fragments of a compact rock of peculiar structuie were present^ See Geol. 
Mag, 1895, p. 4US. (It is represented on Plate I. T. G. 13.) -. 



40 



THE MATRIX OF THE DIAMOND 



cemented by the serpentinous rock may then occur. The 
adjoining shale in place is a black bituminous rock full of 
pyrifce, burning when set on tire. When kept, both un- 
burned and burned specimens after a time become covered 
with alum. The fragments of shale in the peridotite are 
more compact and have lost their shaly character, their 
bituminous or carbonaceous matter and their sulphur. 
The microscope shows that they have also frequently been 
mineralogically altered by the heat of the lava ; having 
lost the character of a shale and become tilled with aggre^ 
gates of micaceous minerals. Often the shale fragment is 
corroded away to a skeleton or shell, filled with the^grouinl- 
mass (fig. 84). In another case a zone of grev kaolin-like 





Fro. 34.— Shale fragment filled with the 
ground-mass 



Fro. 35.— Shale fragment surrounded 
by calcite 



substance occurred around the fragment, while calcite was 
outside of all (tig. 85). 

These enclosures occur of all sizes, from fine powder to 
very large masses. The largest masses are seen only at 
the top of the mine, and are made of shale; they 'are 
called 'floating reef.' In regard also to smaller frag- 
ments, shale is most abundant at the top of the mine ami 
less abundant the deeper we penetrate, bounded fragments 
of granite, mica-schist, and quartzite are found, though 
rarely, and fragments of diabase also occur. All seem to 
have been carried upwards. 

Chemical Composition of the Ground-mass.— k\mo$t all of 
the rock is soluble in acid, a small residue of garnets, 
biotite, bron/ate, perovskite, ilmenite, chromite, &c, re- 
maining. By repeated treatment with hydrofluoric and 



THE MA TniX OF THE DIAMOND 



47 



sulphuric acid all the silicates except garnet are dissolved, 
which with perovskite forms the larger part of the residue. 

The specific gravity of the rock was determined by the 
use of Klein's cadmium solution and Westphal's balance, 
and is somewhat less than the true specific gravity. 

Two varieties were analysed x : — 

I. The least decomposed rock, with few shale enclosures. 

II. The more decomposed rock, with many shale 
enclosures (diamantiferous) . 



Si0 2 (with some Ti0 2 ) 
Fed (including A1 2 3 ) . 

MgO 

CaO ..... 
Na 2 

CO., • 

II 2 (carbonaceous matter, &c.) 

Spec. grav. 



i. 

33-00 
12-00 
32-38 

9-60 

0-67 
705 

600 



ii. 

34-80 

14-10 

30-76 

2-70 

1-40 

5-55 

10-00 

100-70 100-21 

2-734 2-64-2-70 



Since, in Analysis I. 8*1)7 of the CaO clearly belongs to 



the 7*05 CO,, we get : 



or f eliminating the calcite : 







in. 




SiO„ &c. 


• * 


, 3300 


SiO„ &c, 


FeO, &c. 


• « 


, 12-00 


FeO, &c. 


MgO . 


• 


32-3H 


^tgO . 


CaO 


• i 


03 


CaO 


Na 2 . 


• < 


0T>7 


Na 2 


CaCO a (calcite) 


, 1602 


H,0, &c. 


H,0, &c. 


• 


0-00 






100 70 





r 


i. 


39- 


25 


14« 


27 


38- 


51 


o- 


i 5 


o- 


79 


7' 


13 



100-70 



1 The titanic acid (at least 1 per cent.) was not separated from the 
silica, nor the alumina (which was in small quantity in Analysis I.) from 
the iron. The CO., was estimated directly in a CO, apparatus, using dilute 
acid. The carbonaceous (organic) matter ami moisture were determined by 
ignition over a blast lamp, and from the total loss deducting the CO, already 
determined and correcting for the gain of oxygen by the FeO. 



48 THE MAT BIX OF THE DIAMOND 

From Analysis IV. the amount of serpentine in the 
rock can be readily calculated. A typical serpentine ' has 
the composition of 

Si0 2 MgO H,0 
43-48 43-48 13 : 04, 

the water being -fa of the whole. In the Kimberley rock 
freed from calcite the water is only 1 ^ of the whole, so that 
we may conclude that about half of the rock is serpentine. 
The analysis shows that olivine forms the principal con- 
stituent of the remaining portion of the rock. The slight 
excess of silica beyond that required to form olivine 2 
/ SiO., FeO MgO \ , ■ . .. . . L . L , 

V39-12 13-16 44*8oJ' belon 8 s to the blotl te, bronzite and 

garnet present in small proportions. 

The calcite, forming 16 per cent, of the rock, is probably, 
with most of the serpentine, the result of the decomposition 
of the ground-mass. Unless we assume that the lime is 
derived from without, which would be difficult to explain, 3 
it has come from the decomposition of certain lime-bearing 

minerals. With the exception of chrome-diopside which 

is present only in small quantity— the porphyritic crystals 
are practically free from lime. It may have come from 
diopside, melilite, or some other lime-bearing mineral in 
the ground-mass. The small percentage of alumina and the 
mineral associations exclude felspar as a constituent. 4 Calcite 
frequently occurs in serpentine, and is generally regarded 
as the result of the decomposition of a pyroxenic mineral. 5 

1 Rammelsberg, Zeits. Deutsch. Geol. Gesell. xxi. 18g9, p. 97 ; Mineral 
Chemic, Leipzig, Theil ii. 1875, p. 500. 

- Stelzner, * Ueber den Olivin des Melilithbasaltes vom Hochbohl ' 
Neues Jahrb. i. 1884, p. 271. 

' , Surely not; because, where volcanic action has been, gprinffs with 
CaCO., are common. -T. G. B. 

4 It would equally exclude nepheline.— T. G. B. 

5 Doelter, Ueber das Muttergestein der bohmischen Pyropen ; Tschermal- 
Min. Mitth. 1873, p. 13, and other references. 

(It is so sometimes, but it is often infiltrated from without, as in the so- 
called ophicalcite formed from brccciated serpentine.— T. G. B.) 



THE MATRIX OF THE DIAMOND 



49 



The extreme basicity of the rock, the abundance of the 
calcite as a decomposition product, the high magnesia and 
low alkali, the presence of biotite, and more especially of 
perovskite, point to the possible presence of nepheline or 
melilite in the ground-mass. All these characters occur in 
melilite-basalt. 1 Traces of a mineral giving rectangular 
sections occur in the ground-mass, which possibly are to be 
referred to melilite or nepheline, but its altered state pre- 
vents this suggestion from being confirmed with the present 
material. In melilite-basalt, as in the Kimberley rock, the 
pyroxene is chrome-bearing, the perovskites surround 
the olivine ' eineprenglinge,' garnets may occur, and the 
augite may be replaced - by biotite. 3 

The composition of the whole rock, characterised by a 
low amount of silica and a high amount of magnesia, 
together w r ith much lime and little alkalies, may be com- 
pared with that of certain garnetiferous olivine serpentines. 4 
Among unaltered rocks the onlv ones that show similar rela- 
tions between the silica and magnesia are dunite, 5 olivinfels, 6 



1 Stelzner, * Ueber Melilith and Melilithbasalte,' Neues.Jahrb. Beil. 
Bd. ii. 1883, p. 369. 

'-' Tornebohm, 4 Melilitbasalt fran Alno, Stockholm,' Geol. Enren. Ear- 
handl. vi., 1882-83, p. '240. 

3 Professor Koscnbusch, to whom these proofs have been submitted, re- 
marks that it would have been a great satisfaction to Prof. Carvill Lewis 
if he had lived to know that in the State of New York dykes of Alnoite are 
now known to exist in the vicinity of dykes of the Kimberlite character. 
--T. G. B. 

4 Compare serpentine from Zoblitz (Lemberg, Zeits* Deutsch. Geol. 
Gcsell. xxvii. 1875, p. 532) with the following composition : 



SiO, 
39-27 



Fe,0, + Ai,() :J 
8-98 



MgO 

38-78 



Ca() 
M6 



H,0 
11-81 



Compare, also, analyses of many serpentines quoted in Wads worth, TjitJio- 
logical Studies, 1884, table 4. 

5 Dunite from the Vosges (Tschermak, l\[in. Mitth. 1875, p. 187) ; New 
Zealand (Zeits. Deutsch. Geol. Gesell. xvi. 1hC>4, p. 841) ; North Carolina 
(Amer. Joitrn. Sci. xxxiii. 1862, p. 199), &c. 

1 Olivinfels from Steiermark (Tschermak, Mint Mitth. 187'2, p. 79) ; from 
Norway (Kjerulf, Verhandl. Geo/. Reichsanstalt ; , lsiiT, p. 71), &o. 

K 



50 



THE MATRIX OF THE DIAMOND 



and chassignite 1 (an olivine meteorite). The structure 
of the Kimberley rock, as will presently be shown, differen- 
tiates it from these, which are all noncrystalline. The 
rock now described appears to differ from any hereto- 
fore known. Picrite-porphyrite is practically a felspar-free 
melaphyre, or, perhaps in deference to its hornblende, it 
may be called the effusive form of the rock named camp- 
tonite by Eosenbusch. Picrite-porphyrite is also an augitic 
rock, and contains less magnesia than the Kimberley rock. 
Limburgite, the neovolcanic equivalent of picrite-porphyrite, 
is likewise an essentially augitic rock, being a non-felspathic 
basalt, 2 and is also much poorer than the Kimberley rock. 

There appears to be no named rock-type having at once 
the composition and structure of the Kimberley rock. For 
this reason, as also on account of its importance as the 
matrix of the diamond, it is now proposed to name the 

rock Kimberlite. 

Kimberlite may be described as a porphyria volcanic 

peridotite of basaltic structure, or, according to Eosen- 

busch's nomenclature, the palseovolcanic < ergussform ' of a 

biotite-bronzite-dunite, being an clivine-bronzite-picrite- 

porphyrite rich in biotite. Had it less olivine and more 

rhombic pyroxene it could be classed among the picrite- 

porphyrites, and be called a saxonite-porphyrite. As it is, 

it is more nearly related to a dunite-porphyrite. Prof. 

Judd has described a porphyritic dunite, but that is a holo- 

crystalline deep-seated rock of entirely different structure 

from the rock under consideration. In fact Kimberlite is a 

rock sui generis, dissimilar to any other known species. 

Three varieties of Kimberlite may be distinguished: 

» Vauquelin (Ann.Phys. Chim.i. 181G, p. 49) ; Damour (Paris, Comptcs 
Benchis, lv. 1802, p. 591) ; Tschermak (Wien. Akad. Sitzbcr. lxxxviii. 1883 

(Abth. i.), p. 861). 

« This must be understood in the sense that felspar has not yet separated 
from the glassy basis. From the chemical composition of the rock, it is 
reasonable to conclude that limburgite, with a different environment, would 
appear in the form of a picrite ; i.e. a rock containing some felspar, but not 
so much as in a dolerite. — T. (i. B. 



THE MATRIX OF THE DIAMOND 



51 



(1) Kimberlite proper, a typical porphyritic lava ; (2) Kimber- 
lite breccia, the same lava broken and crushed by volcanic 
movements and crowded with included fragments of shale ; 
(3) Kimberlite tuff, being the fragmental and tufaceous 
portion of the same volcanic rock. These varieties pass 
by insensible gradations one into another, so that no 
sharp line can be drawn between them, and all occur 
together in the same neck or crater. The Kimberlite 
breccia forms by far the greater' portion of the rock, and is 
rich in diamonds. It is traversed by dykes of Kimberlite 
proper, and contains streaks and patches of softer * soapy ' 
material, which appears to be the Kimberlite tuff. The 
deeper portions of the Kimberlite breccia become more 
compact as though passing gradually into Kimberlite proper. 
The so-called 'blue ground' has also been analysed, 
but being so thoroughly altered, the analyses are of small 
scientific value. 

Perhaps the most interesting chemical observation con- 
cerning this 'blue ground' was that made by Sir H. E. 
Eoscoe. He found l that on treating it with hot water an 
aromatic hydrocarbon could be extracted. By digesting 
the ' blue ground ? with ether, and allowing the solution 
to evaporate, this hydrocarbon was separated and found to 
be crystalline, strongly aromatic, volatile, burning with a 
smoky flame, and melting at 50°C. 

Structure. — The structure of Kimberlite, to which sub- 
ject we may now proceed, is its distinguishing and charac- 
teristic feature, differentiating it from ordinary serpentines 
and peridotites, if not from all other terrestrial rocks. The 
structure can only be compared with that of certain 
meteorites. 

It may be described as a porphyritic brecciated struc- 
ture. While evidently the structure of an eruptive rock, 
it at the same time shows clear proof of mechanical disturb- 
ances during or after its cooling. According as the por- 



1 Manchester, Lit. Phil. Soc. True. \>iv. 1885, p. •">. 



K '1 



52 THE MAT BIX OF THE DIAMOND 

phyritic or the brecciated structure happens to predominate 
in the section under examination, the observer varies in 
his opinion as to whether the rock is a lava or a tuff. 

Cohen, Hudleston, Moulle, and others, believed it to be 
an igneous tuff, while Dunn, and Maskelyne and Flight con- 
sidered it to be an eruptive gabbro-like rock. 

When comparatively free from enclosures the porphyritic 
structure may be as distinctly shown as in a basalt. 
The greater mass of the porphyritic crystals (the ' einspreng- 
linge ') are the olivines, which often have distinct crystalline 
form. These are, as already stated, more frequently 
rounded and like the olivines in basalts, and may show the 
action of a corrosive magma. Biotite, bronzite, garnet and 
other substances also form comparatively large crystals, 
usually rounded, and, with the olivines, lie separately in a 
more or less isotropic ground-mass made mainly of a serpen- 
tinous mineral. The rock therefore is not noncrystalline, 
but belongs to the class of volcanic or effusive rocks 
(' erguss-gesteine '), characterised by idiomorphic porphyritic 
crystals floating in a ground-mass. 

That the rock was a true igneous lava, and not a mud 
or ash, is indicated by the following facts : — 

1. The minerals and their associations are those character- 

istic of eruptive ultra-basic rocks. 

2. The porphyritic crystals are idiomorphic as in volcanic 

rocks. 
8. The corrosion cavities (' einbuchtungen ' ) in the por- 
phyritic crystals are due to solution by the hot magma. 

4. The character of the bronzite and ditfpside is similar 

to that in meteorites and eruptive rocks, but not in 
metamorpbic or plutonic rocks. 

5. The occurrence of a ground-mass and of traces of glass. 

6. The traces of a second generation of minerals (pyroxene ?) 

in the ground-mass. 

7. The occurrence of fragmentary enclosures of the adjoining 

rock and of deep-seated rocks, and the evidence of 
alteration by heat which these enclosures exhibit. 



/ 



// 



THE UATMX OF THE DIAMOND 



53 



8. The traces of a fluidal structure shown on polished 

specimens. 
<). The identity of the rock with one in Kentucky, which is a 

true eruptive dyke, and with others in the Vaal River, 

which also form dykes. 
That it is not a tuff is shown by the entire ahsence of 
stratification, of clayey or ashy hands, of water-worn frag- 
ments, of cementing material, and by its geological position : 
not as an overflow mud deposit, but in the very neck of a 

volcano. 1 

The brecciated structure of the rock is shown not only 
in the abundance of angular fragments of shale it contains, 
but also in the broken and angular character of many of 
the porphyritic crystals in it, and the mechanical manner in 
which they seem to have been sometimes pushed together. 

Yet the structure is not a purely mechanical one, such 
as is the case with certain ancient rocks which have been 
subjected to heavy pressure. A so-called mechanical-por- 
phyritic structure is well known in deep-seated peridotites, 2 
being particularly well marked in the variety named olivin- 
fels.° These, as Brogger 3 and Reusch have shown in Nor- 
way, are often so crushed as to resemble a sandstone. 
Here, however, under the microscope the so-called ' cata- 
clastic' structure, 4 or ' mortel-structur,' 5 whereby the 
outer portions of the crystals are smashed into a mosaic- 
like band (as in < augengneiss,' &c.) can always be seen. No 
traces of this cataclastic structure occur in the Kimberley 
peridotite. The olivines have no mosaic borders or ends, no 
< eyes' of them are made, and their rounded form is certainly 



' (Bat suppose the rock were an agglomerate? This appears to me 
equally consistent with all the reasons given above, except, perhaps, 8 and 
9, of which the former is very dubious, but the latter no doubt »^W' 
because an agglomerate does not usually have a dyke-like habit.- -1. tx. v.) 

- llosenbusch, Mikrosk. Pliifsiogr. ii. 1*87, p. -73. 

3 Neues Jahrb. 1880. ii. p. 187. 

4 Kjerulf, Christiania, Nyt. Mag. Naturvid. xxix. 188o, p. 215. 

• Tornebohn, Stockholm, Ueol Forcn. FUrhandU v, 1880-81, p. 233. 



54 THE MATRIX OF THE DIAMOND 

not due to pressure. The brecciated structure, therefore, 
whatever its cause, is not due to pressure. 

Several causes may produce brecciation in a volcanic 
rock. It may bedue : — 1. To the rapidcooling and consequent 
shrinking and cracking of a fluid lava ; 2. To the contact of 
the moving lava with the adjoining rock which is carried 
along with it and broken up to form a so-called friction 
breccia (' reibungsbreccia') ; 3. To subsequent explosions and 
movements in the crater of the volcano. It is quite possible 
that in the present instance all three of these causes may 
have operated. 

As to the first cause, the words of Dr. Wadsworth, 1 if 
applicable, seem prophetic. After explaining the brecciated 
character of meteorites as due to rapid crystallisation, he 
says : ' If we could find rapidly cooled, unaltered terrestrial 
peridotic rocks, I should expect to find in them the chon- 
dritic structure, the same as the Esther ville meteorite 
possesses the structure of an unaltered terrestrial peridotite, 
and the meteoric pallasites possess that of the terrestrial 
ones.' Eoth 2 speaks of the formation of lavas and slags 
which fall apart on cooling. 

The second process, which causes a * friction breccia/ 
is well known in many volcanic districts. It is seen on 
approaching the vent of the volcano. Naumann 3 has given 
some excellent examples of this in Saxony, where in the 
border between porphyry and shales, great masses of the 
breccia, the so-called < Brockengesteine ' is formed, and the 
mass of the enclosed slates may predominate over the mass 
of the porphyry. 

The third process, the result of successive explosions in 
the same crater, is also common in volcanic districts. In 
this case, not only are fragments of the adjoining rock en- 
closed in the lava, but the older and hardened magma 
itself is broken up and imbedded afresh in the new erup- 

1 Lithological Studies, 1884, p. 111. 

- Allg. unci chcrn. Gcol. Berlin, ii. 1883, p. 207. 

3 Lehrbuch der Gcognosic, Leipzig, i. 1858, p. 917. 



THE MATRIX OF THE DIAMOND 55 

tion. In this case the old lava forms the larger part of the 
breccia, anil the final composition and structure is not un- 
like that of a tutf. It is of course just this material which, 
when ejected in the form of dust or mud, does make the 
stratified ashes called tuff. This kind of breccia occurs m 
the Euganean Hills, 1 in Italy,* and perhaps m ^ales. ! 

According to Chaper,' who has studied the geology 
of the Kimberley mines, the eruption has taken place at 
many successive periods; all his observations pointing 
to a series of eruptions, between each of which there 
was time for the volcanic mass to consolidate. He says 
that the «reat irregularities so puzzling to the miners are 
thus explained, and that at Bulfontein and Du Toits Pan 
it is possible to make out a chronology of the various 

eruptions. , . ., . 

If this last is the principal cause ol the breccia it is 
no wonder that the rock should so closely resemble a tuff. 
It is of course, difficult to draw the line between a brecciated 
lava' and a tuff, but in this instance everything points to 
its lava-like character. The tuff would lie outside of the 
volcano, the brecciated lava in its vent. The conception 
of a true porphyritic lava, afterwards broken by paroxysmal 
eruptions, seems perfectly to explain the nature of the 
remarkable rock which is now under discussion. Certain 
so-called ' soapy ' bands in the mine probably represent the 
true tuff. Just as the limburgite of the Kaiserstuh district 
alternates with beds of tuff, so here it is probable that 

■ Reyer, Ftdk der Eruptive; Die Euganatn. fit is often very well 
exhibited in the dykes of basalt cutting through lower ™^™™% 
near Burntisland, Scotland. See, for other cases, i'roc. Geol. Auoc vu. 

No. 2.-T. Q. B.] 

- Bonnet*. Joum. Geol. See. «xv. 1879, p. 311. Fit may also 
be produced'oy more solid parts of the lava being rupture* and swept along 
by the onward pressure of the more liquid mass, the result being ofteij 

called a fluxion-breccia. T. G. IV aiamant 

• • -i — >r\ inK * Villi' l»' ic ; lnillCS lit 1 UltlllldlU 

' Bull. Soc. Min. de France, 11. Ib79, i>. 195, bui les mines 
de l'Afrique Australe.' 



50- THE MATRIX OF THE DIAMOND 

Kimberlite tuff occurs together with the Kimberlite 
breccia. 

A comparison of the Kimberlite with known ashes or 
tuffs, Professor Kosenbusch having kindly placed his 
collection at my service for this purpose, has failed to 
establish any analogy with them, and I am compelled 
to differ from Professor Cohen and others who speak of 
it as ash, mud, or conglomerate, and to regard it as a true 
eruptive lava. 

The structure of the African Kimberlite is equally 
shown in the Kimberlite from Elliott County, Kentucky, 
and with that from Syracuse, New York. I have compared 
the Kentucky rock with the African rock directly. Dr. 
Williams has published a photograph of that from Syra- 
cuse. 1 In mineral composition, in eruptive character, in 
structure, in enclosures, the three rocks are identical. As 
the Kimberlite of Kentucky and New York State occurs in 
dykes, not volcanic vents, it becomes all the more certain 
that the porphyritic structure is an origins 1 one characteristic 
of the rock. 

Although, as already stated, the peculiar character of 
Kimberlite is shared by no other terrestrial rock, it is 
of high interest to find that in structure it resembles 
meteorites of similar composition. Attention has already 
been called to the likeness of some of its minerals to 
those in meteorites, and its chemical composition has also 
been shown to be closely related to that of the olivine 
meteorite called chassignite. 

If we were to replace the ground-mass of Kimberlite by 
native iron, we should get a rock nearly allied in both struc- 
ture and composition with the well-known class of meteorites 
known under the name of chondrites. These meteorites 
are both porphyritic and brecciated, and when the breccia 
structure is well developed it has given rise to the same 



' For notes upon specimen* afterwards obtained from theae localities by 
1 rotessor Lewis, see Section 111. 



THE MATH IX OF THE DIAMOND 57 

discussion as Kimberlite, as to whether they are tuffs or 
lavas. Haidinger was one of the first to describe the 
so-called meteorite-breccias, and to show that not only are 
angular fragments of other rocks frequently enclosed in the 
olivine rock, but that the meteoric rock itself is often 
broken into angular and rounded fragments cemented 
together, as if a volcanic tuff. Tschermak » holds to the 
tuff-like character of certain meteorites, yet remarks that— 
1 There occur passages into the tuff structure, so that the 
same stone may be designated by one observer as crystalline, 
by another as clastic' Another structure in these olivine 
meteorites is the occurrence of rounded masses of olivine 
or of olivine and enstatite, called the chondritic structure. 
The origin of this has given rise to much discussion. A 
chondrus may consist of a single optically continuous mass 
of olivine, or it may be polysomatic, that is, due to a number 
of individuals. 

Polysomatic chondri of olivine occur in the Kentucky 
Kimberlite. The olivines are laid together, as if in a 
mosaic, the whole forming an irregular sphere. This 
is identical with a granular chondrus in a meteorite 
from Seres figured by Tschermak.- Glass which occurs in 
these chondri occurs also in a chondrus from Kimberley. 



1 Die mikrosk. Beschaff. dcr Metcoriten, Stuttgart, 1885, p. 3. 
a Ibid. (Plate VIII. fig. 2.) 



58 



SECTION III 

KIMBEBLITE FROM THE UNITED STATES 
By PROFESSOR T. G. BONNE Y 

Two rocks from the United States, specimens of which were 
in Professor Carvill Lewis' collection at the time of his death, 
present, as will be seen hereafter, a very close macroscopic 
and microscopic resemblance to the diamond-bearing rock 
from South Africa. One occurs at Syracuse, New York ; 
the other about six miles south-west of Willard, in Elliott 
County, Kentucky. For the most recent information relat- 
ing to the former rock we are indebted to the late Professor 
G. H. Williams; the latter has been described by Mr. 
J. S. Diller. 

1. Rock of Syracuse, New York. 1 — There are two types 
of this rock, according to Professor G. H. Williams ; one of 
these is a very dark green, almost black, rock, with minute 
specks of glistening mica, occasional larger plates of a brass- 
yellow mineral (4x6 mm.), and a few small masses of a 
lighter green more compact serpentine with a sharp crystal 
form. The other is paler in colour, composed of a dense 

^ -- — — ' - ■ - . _ 

1 Literature.— G. H. Williams, Science, March 11, 1887; Amcr. Journ 
Sci. xxxiv. 1887, 137 ; Bull. Geol. Soc. Amcr. i. 1890, p. 533. He cites 
Vanuxem (Third Annual Report, 1839, and Final Report on Geol. of Third 
District of New York, 1812) ; Lewis Beck (Report on Mineralogy of New 
York, 1842) ; T. S. Hunt (Mineral Physiography and Physiology, 443-447) • 
and Amcr. Journ. Sci. ii. xxvi. 1858, 237 ; Geological Hist, of Serpentines 
(Trans. Roy. Soc. Canada, i. 174); and J. D. Dana (Manual of Geology, 
p. 233, third edition), as referring to it more or le& in detail. 



KIMBEBLITE FROM THE UNITED STATES 



59 



compact base containing numerous lighter spots, with a 

sharp crystal outline, thus producing a porphyritic structure. 

Some singular blood-red patches are scattered through 

this rock. The first type, under the microscope, appears 

as a medium-grained aggregate of brown mica, of octahedral 

crystals of two minerals— one yellow and transparent, the 

other black— of green or colourless terpentine, and of 

carbonates. Through this matrix occasional larger crystal 

forms are scattered. In spite of nearly all the substance 

of the rock being secondary, these preserve the shape of 

crystals. Among the minerals present Professor Williams 

identities olivine or enstatite ; the latter being completely, 

the former mostly, replaced by serpentine. The mica is 

the peculiar brown biotite, well known to be characteristic 

of eruptive peridotites, without a definite crystal form, and 

often with a bleached peripheral zone. Of the octahedral 

minerals, the opaque are usually chromite, but a few may 

be magnetite, the transparent are proved to be perovslute. 

The second type of this rock, under the microscope, is 
identical with the former, except as regards structure. 
The ground -mass is liner grained, thus throwing the 
characteristic crystal forms of the olivine and enstatite 
into sharp relief; the octahedral crystals are much 
smaller than in the other rock and are confined wholly to 
the ground-mass ; the brown mica is less abundant. ' The 
persistence of structure in this rock, in spite of the 
profoundest chemical changes, is remarkable. In one 
porphyritic specimen, the ground-mass is almost al car- 
bonate, the mica has become quite colourless, and the olivine 
crystals are changed to a perfectly isotropic colourless 
substance, enclosing the sharpest possible rhombohedra ot 
dolomite ; in fact none of the original components remain, 
except the chromites, and yet the structure is just as sharp 
and characteristic as in a specimen,' of which Professor 

Williams gives a figure. . . 

The rock, when Professor Williams wrote his earlier 
paper, was no longer visible, being concealed beneath 



GO K1MBEULITE FROM THE UNITED STATES 

a lawn and a street. His description was founded upon 
observations made and specimens collected, about 1887, 
by Professor Oren Boot, who found it to be associated with 
shales and limestone belonging to the Onondaga salt-group, 
and considered it, for reasons which he gives, to be intrusive 
in them. 

In a later paper 1 Professor Williams adds some 
interesting details. In cutting some deep sewers, ' two 
admirable sections ' had been exposed. In these it was seen 
that the serpentine formed a dyke, cutting perpendicularly 
across the nearly horizontal strata of limestone, forcing its 
way in places between them, and, in one of the exposures, 
considerably disturbing those in its immediate vicinity. 
Much of the serpentine was full of angular fragments of 
other rocks embedded in it, sometimes at least one-third of 
the face of a block being occupied by fragments. Most of 
these, but by no means- all, are bits of the adjacent lime- 
stone. One, for instance, is a lar^e fragment of black 
shale (probably Utica shale), which here is over 1,000 feet 
below the surface. Another is a fragment of an acid 
crystalline rock, granite or gneiss, which must lie over 
2,000 feet below the surface. Granitic and syenitic frag- 
ments were also mentioned by the earliest observers. All 
of the included limestone fragments show signs of contact 
metamorphism, and the new minerals, thus produced, have 
a zonal arrangement. 

Professor Williams is of opinion that the eruptive 
rock, which is now represented by the serpentine, must 
have differed much from its present composition as repre- 
sented in analyses furnished by Professor James Ball, 
which he quoted in the earlier memoir. The specimen 
consisted of carbonate of lime 34*77, carbonate of magnesia 
2-73, and serpentine 62-5. The composition of the last 
was as follows : — 



Bull. Gcvh fifoc. Amcr. i. 1890, p. 533, 






KIMBEBLITE FROM THE UNITED STATES 61 

Si0 2 4(H >7 .. 

Al a 3 518 

Fe() 8 * 12 

MgO 82-61 

H,0 1277 

99-30 

(2) Rock <>f Elliott Countji, Kentucky:— 
This rock occurs between Isom and Critche's Creeks, 
near Fielden Post Office, six miles south-west of Willard, 
in Elliott County, Kentucky. Mr. Diller describes it at 
some length in the ' Bulletin of the American Geological 
Survey/ l and, more shortly, in the American Journal of 

Science* 

It was discovered by Professor A. E. Crandall, who 
states that it has a very limited extent laterally, and so 
readily disintegrates as not to form a noticeable feature in 
the topography. ■ It appears to extend in two diverging 
lines from Critche's Creek into the valley of Isom's Creek, 
with several minor offshoots of undetermined, but doubt- 
less limited, extent, possibly no more than wedge-like 
projections from the main dyke between the strata of the 
coal measures, which make up the whole height of the 
hills of this region. The whole length of the dyke in its 
greatest surface extension appears to be less than a mile, 
with a width of from a few feet to 50 feet or more/ :i The 
rock, according to Mr. Diller, is compact in structure, dark 
greenish in colour, with a specific gravity of 2-781, having 
embedded in it many grains of yellowish olivine, um- 



1 No. 38 (with map and illustrations). 

- Vol. xxxii. p. 121. See, also. Science, 1885, p. 85. 

3 This statement is mainly an inference, as pointed out by Mr. Diller, 
from the presence of pyrope and ilmenite in the soil. The visible outcrops 
of the rock are only live in number- three of them in a line about three fur- 
longs long ; the others being about live furlongs away in opposite directions 
from one end of it, which happens to be the spot where the rock is in best 
preservation : they are more or less oval in shape. 



62 



KIMBEBLITE FROM THE UNITED STATES 



formly distributed throughout the mass. These, however, 
occasionally disappear, and the whole is serpentine. 
This olivine and the serpentine together form nearly 75 
per cent, of the rock. Besides them other minerals 
appear in the hand specimen, the most important being 
pyrope and ilmenite; a few scales of biotite may be 
observed. Near the exposed surface the rock becomes 
yellowish, due to the oxidation of the iron, and softer, so 
that it readily disintegrates. 1 The garnet and much of 
the ilmenite withstand the atmospheric influences, and are 
found quite fresh and abundant in the sand resulting from 
the disintegration of the peridotite. The specimens from 
some localities are quite free from included fragments, 
while those from another ' are full of fragments of shale, 
which have been greatly indurated and metamorphosed in 
the operation.' In the best preserved specimens (which 
also are free from rock fragments) Mr. Diller estimates the 
composition to be as follows : — 



Primary 


minerals 


Per cent. 


Secondary mini 


;rals 


Per cent. 


Olivine 


• 


• 


40 


Serpentine . 


• 


. 30-7 


Enstatite 


. . 


• 


1 


Dolomite . 


• 


. 14 


Biotite 


• • 


• 


1 


Magnetite . 


• 


. 2 


Pyrope 


• • 


• 


8 


Octahedrite a 


• 


. 1-1 


Ilmenite 


. • 


• 


2-2 








Apatite 


• • 


• 


trace 









He gives a figure of a microscopic section from which 
it would appear that the larger included minerals are 
somewhat irregular in outline, size, and distribution. The 
olivine grains are generally irregular in form, varying from 
0*1 to 1-5 mm. in diameter, and penetrated by many 
lissures. Occasionally, however, they occur in short 
prisms, terminated by brachydomes, the usual planes 
being suppressed. The structure of the matrix appears to 
be fine-granular. The alteration of the olivine to serpen- 



1 Compare the ' yellow ground ' of the mines at Kimberley. 

" A synonym of anatase (TiO,) ; and corresponding with the perovskite 



' 



of Williams. 



K1MBEBLITE FBOM THE UNITED STATES 68 

tine takes place rapidly in the cross fractures approximately 
parallel to the base, but very slowly along the numerous 
minute fissures in the prism zone. Cleavage parallel to 
the brachypinacoid is barely discernible. Magnetite is 
excluded in the usual manner, and in some cases dolomite 
appears as an ultimate product of alteration. The en- 
statite has an irregular (corrosion) border. The biotite is 
dark coloured, is strongly dichroic, and is sometimes sur- 
rounded by a secondary border of biotite (differing in 
optical properties) and of magnetite. The pyrope occurs 
in spherical and ellipsoidal grains, varying from 1 to 12 mm. 
in diameter, of a clear, deep-red colour, its specific gravity 
being B*(>73. It is often surrounded by a border, the 
outer band of which is commonly rendered opaque by a 
dark powder, the inner one being a greyish or reddish- 
brown colour, generally fibrous in structure (the substance 
named kelyphite by Schrauf, but shown by Lasaulx to 
be a mixture of several minerals, chiefly of the pyroxene 
and ampbibole groups). Of the other minerals, the 
octahedrite occurs in yellowish clouded grains, ranging 
in size from -004 to -06 mm. in diameter. The dolomite is 
irregularly distributed. Of the serpentine there are two 

forms. 

This peridotite cannot be seen in contact with the 
adjacent sandstone and shale ; but within a short distance 
from it both appear to be indurated, and the latter in some 
cases to be converted into a kind of spilosite. The frag- 
ments of shale included in the peridotite are always 
surrounded by a border of colourless mica, its scales being 
intricately intermingled, and have undergone other mineral 
changes, generally on a minute scale. On a review of tbe 
whole evidence, Mr. Diller concludes that ' the peridotite 
is a truly eruptive rock, which has been forced up through 
the carboniferous strata.' 

At the end of the paper Mr. Diller gives a series of 
analyses of the adjacent sedimentary rocks, of the peridotite, 
and of the minerals contained in it. 



V 



64 



KIMBEBLITE FROM THE UNITED STATES 



The following represent the peridotite : — 

i. 



Si0 2 
Ti0 2 

PA 

Cr,0 3 

A1 2 0, 

Fe,0, 

FeO 

MnO 

NiO 

CaO 

MgO 

K 2 

Na,0 

H s O (at 110°) 

CO., 

so 3 

Total 

S.G. 



29-81 
2-20 
0-35 
0-43 
2-01 
5-16 
4-35 
0-23 
0-05 
7-6!) 

32-41 
0-20 
0-11 
8-92 
6-66 
0-28 



100-80 



2-781 



11. 
29-43 
1-48 
trace 
014 
2-86 

• • • • • • 

9*06 
•••••• 

or>o 

94 
81-66 

0*65 
078 
1090 
565 
0-30 

100*15 l 



2-697 



To these notes may be added a few remarks on the 
specimens which I find in Professor Lewis' collection :— 

The hand specimen [436] labelled ' From James Street, 
Syracuse, N. Y. (G. H. W. col. Fel>. 1888)' is a dark- 
coloured rock of a greenish tint, slightly mottled in one or 
two places with a yellower green hue, compact in structure, 
dull, but with fairly numerous rather rounded spots, up to 
about one-sixth of an inch in diameter, with a more 
glistening lustre. The specimen is traversed by a thin 
whitish vein. In fracture and general aspect it resembles 
a serpentine, or something between a serpentine and a 
diabase, except for the slight irregularity in the ' por- 



Includin^ 020 of sulphides. 



KIMBERLITE FROM THE UNITED STATES 65 

phyritic ' structure. A slice has been prepared for micro- 
scopic examination ; but here, as in the case of the others 
mentioned below, a brief notice will suffice, after Professor 
Lewis' elaborate description of the Kimberley rock, for 
the general resemblance is very strong. In this slice we find 
a number of grains, rather variable in size and form, some 
approaching idiomorphic, others rounded or apparently 
broken, but all serpentinised. Most of them were formerly 
olivine, but it is possible that enstatite also may have been 
present. There are various differences of detail in the 
colour and minuter structure of the serpentine, in the dis- 
tribution and arrangement of the iron oxide, and the like ; 
but on them it is needless to dwell. These larger grains 
are scattered about in a more or less granular matrix, 
apparently identical with that of the Kimberley rock, in 
which serpentine and a carbonate, probably calcite with 
some dolomite, are important constituents. One part of 
the slice suggests the presence of fragments of a peridotic 
rock, embedded in a matrix of similar condition ; but 
whether this is significant of a pyroclastic structure or of a 
fluxion breccia is open to question. Here, also, is a small 
1 patch ' of rather rounded mineral fragments, which seem 
to be a felspar. I 

The rock from Kentucky is represented by the following I 

specimens : — 

(a) [435, 1.] < Dyke I., Elliott Co. (Crandall).' A rock 
resembling that from Syracuse in colour and aspect, but the 
fracture is a shade rougher, the rounded spots run to a 
slightly larger size, being not seldom about one-fifth of an 
inch in diameter ; they are less lustrous than in the other 
case, and of a yellowish-green colour (similar to that in the 
mottling of the other specimen and resembling that of 
olivine), and thus lighter than the matrix. Except in this 
respect the two specimens are very similar. Microscopic 
examination shows that this rock closely resembles one of 
the best-preserved specimens from Kimberley, The olivine 

F 






I ' 66 KIMBEBLITE FBOM THE UNITED STATES 

I generally is more rounded than in the last case, and a con- 

I siderable amount of the original mineral still remains, 

1 especially in the larger grains ; that is, they are about half 

I olivine, half serpentine, exhibiting the usual structure. There 

I is one grain which appears to be a monoclinic pyroxene, con- 

I tabling two or three flakelets of a micaceous mineral ; also, 

I a small grain of the usual brownish mica, a garnet with the 

I outer zone of rich brown kelyphite, already described, with 

; two others--which possibly may be the same mineral more 

I completely altered— and two or three smaller deep-brown 

I grains resembling chromite. One or two irregular patches, 

1 consisting of a carbonate and some small minerals (zeolites) 

[| • are very like the irregular cavities in some scoriaceous 

rocks, wh*n these become converted into amygdules. I 
suspect the presence of a small rock fragment consisting of 
little roundish grains of olivine (or possibly malacolite) in 
a minutely granular matrix, of which I can hardly venture 
to say more than * probably basic igneois.' 

(b) [435, 2.] The label with this specimen (a printed 
one on thick paper) is partly effaced by rubbing ; it has the 
words ' Kentucky Geological Survey . . . and Bureau of 
(? emigration). Frankfort, Kentucky, U.S.A.' (the effaced 
part being apparently a date, perhaps 188G). It is not dis- 
tinctly stated to be from the above locality, but I think 
there can be no doubt on that point. It is practically 
identical with the last-named, except that the yellowish- 
green spots run a shade larger, occasionally almost 
one-quarter of an inch. Under the microscope the rock 
appears very similar to the last described, but the olivine 
is rather more serpentinised ; garnet as before ; one or two 
patches of calcite with a tuft or two of an acicular zeolite, 
suggestive of cavities of some kind ; part of the matrix 
is tinged with green, this apparently being due to the 
presence of minute scales of a chloritic mineral. 

(e) [437.] This specimen bears the label, ' Elliott Co., Ky. 
(Diller).' The matrix is slightly more compact than in 
the case of the last two the yellowish spots are not quite 






K1MBBRLITE FROM THE UNITE!) STATES G7 

so frequent, or ho large generally, though one, which shows 
a moderately good cleavage and is apparently olivine, attains 
to quite a quarter of an inch. It has a distinctly rounded 
outline. Mica also is more plentiful in this specimen, 
occurring generally in small rounded Hakes ; but these in one 
or two cases are about one-fifth of an inch in diameter. It is 
distinctly brown in colour. In microscopic structure the 
rock is like the last, but without any garnet or spots 
suggestive of filled-up cavities ; there are also one or 
two semi-opaque grains, minutely granular in structure, 
which are possibly fragments of some rather compact and 
decomposed rock. 1 

The above hand specimens from both Syracuse and 
Elliott Co. are perhaps a little more like a porphyritic 
igneous rock than those which I have seen from Kimberley, 
owing to the absence of distinct rock fragments and the 
more uniform size of the included minerals ; and the same 
may be said of their microscopic structure. They are very 
like serpentine, but the points to which attention has been 
called produce a difference — marked, though not easily ex- 
pressed in words — from the normal specimens of that rock. 
This also is very perceptible in looking at the thin slices 
with the unaided eye or with a common pocket lens, when 
they are held up to the light. The rather rounded outline 
of the enclosures, their unequal size and distribution, give 
them a fragmental, rather than a normal porphyritic, 
aspect. I believe that had I been asked to guess what the 
rocks were, from the evidence of the hand specimens and 
from this mode only of studying the slices (i.e. without 
actually using a microscope), I should have answered 
* probably a non-scoriaceous unstratified tuft.' 






1 See Plate II. for a figure of a portion of thi> specimen. 






NOTE 

The portions of Professor Lewis' manuscripts which, as 
explained in the Preface, have not been printed, brought 
out more clearly one point in regard to the origin of the 
diamond than is done in the two papers included in this 
work, though I remember he laid stress on it in giving a 
summary of the second paper at Manchester. This was 
the intimate connection of peridotite (or serpentine) with 
the diamond, which he regarded as being in the relation of 
cause and effect, at least in South Africa and in Kentucky, 
where carbonadoes occur under similar conditions. This 
will appear from the report of his paper printed in the 
•Geological Magazine' (1888, pp. 129-131). It may 
suffice to quote the concluding sentence : * All the facts thus 
far collected indicate serpentine in the form of a decom- 
posed eruptive peridotite as the original matrix of the 
diamond.' Professor Lewis, I believe, thought that, owing 
to the basic nature of the peridotite, the carbon in the 
sedimentary rock with which it came into contact was 
less likely to be oxidised than it would be by more acid 
intrusives, but this opinion, so far as I know, is not ex- 
pressed in his published papers. 

I may add that in 1896 the workings in the De Beers 
Mine had reached a depth of over 1,500 feet. They have 
ceased to work the diamond-bearing rock by excavating it 
vertically downwards from the top of the ' pipe,' but sink 
shafts through the < country rock ' (shale, quartzite, and 
^melaphyre'), from which they drive levels into the pipe 
itself, removing its contents by means of these, as it were, 



) 



NOTE 



09 



layer by layer. While the last sheets of this book were in the 
press Sir J. 13. Stone, M.P., F,G.S.,sent me a collection of 
specimens which he had recently received from this mine, 
among which were pieces of the diamond-bearing rock, of 
which the deepest was labelled 1,400 feet, and I saw blocks 
from nearly as far down in a collection shown to me by 
Mr. W. Crookes, F.R.S. A particularly well-preserved 
specimen which he has lent to me for study came from 
1,320 feet. 

He has also favoured me with a copy of a section re- 
presenting the workings in this De Beers mine. The shaft 
has reached a depth of quite 1,500 feet, and from it the 
low T est level is being driven. The section of the ' country 
rock,' outside the ' pipe ' containing the diamond-bearing 
breccia, is as follows : (1) superficial debris, (2) basalt, (3) 
black shale, (4) 'melaphyre,' (5) quartzite, (6) ' slate' — pro- 
bably only a hard shale, (7) quartzite and ' slate.' Dykes 
(probably basaltic) pierce into (5), through (6) and (7). 
The ' melaphyre ' (4) is about four hundred feet thick. The 
area of the workings is twenty-two acres. It is the least 
of the four mines mentioned on page 1 ; Du Toits Pan, 
the largest, being forty-live acres. Since Professor Lewis 
wrote, another important mine (the Wesselton) has been 
opened ; it is included within the same circle as the last- 
named. 

T. G. B. 



INDEX 



Aerinite, 15 

Africa (South), first diamond found 

in 1870, 1 
Age of diamond-bearing ' pipes,' 7 
Agglomeratic matrix, 53 
Analyses, diamond-bearing rock, 5, 

47 
Analysis, bronzite, 20 

— Kimberlite, 61 

— Mica, 28 

— Peridotite, 64 

■ — Serpentine, 61 

— Smaragdite, 19 

— Vaalite, 28 
Anatase, 62 
Apatite, 37 

* Augengneiss,' 53 



Ball, J., 60 

Bastite, 19 

Baumhauer, E. H. von, 32 

Beck, L., 58 

Becke, F., 24 

1 Blue ground,' 3 

— the diamond matrix, 44 
Bonney, T. G., 55, 68 

— on Kimberlite, 58 
Boricky, E., 34 
Bourgeois, 35 
Breithaupt, A., 36 
Brewster, D., 44 

1 Brockengesteine,' 54 
Brogger, W. C, 53 
Bronzite, 4, 19 

— analysis, 20 
Bulfontein Mines, 1 
Butler, P. J., 44 



Calcite, 38 
' Calc-tuftV 38 
Cataclastic structure, 53 



Chalcedony, 39 

diaper, M., 55 

Chassignite, 50 

Chondrites, 56 

Chrome-diopside, 21 

Chromite, 36 

Cohen, E., 3, 7, 38, 52 

Colesberg Kopje, shale in volcanic 

pipes, 4 
Colonial Exhibition, 3, 8 
Connecticut, smoky quartz, 43 
Cooper, G. C., 44 
' Country rock,' 3, 8, 68 
Crandall, A. li., 35, 61 
Crookes, W., 69 
Cross, C. W., 26 
Cyanite, 39 



Dana, J. D., 58 
Dathe, E., 26 
Davies, T., 4 
De Beers Mines, 1, 8, 68 

— 1885, section, 8, 69 
' Demantoid,' 28 
Descloiseaux, A., 32, 44 
Diallage, 4 
Diamond, 40 

— history of, 1 
Diamond-bearing peridotite, 1 
' pipes,' age of, 7 

— matrix, 44 

Diamonds, liquid carbonic acid in, 
43 

— minute, 41 

— Russian, 29 
Diller, J. S., 35, 61 
Doelter, C, 22, 48 
Doll, E., 44 

' Dry diggings,' 2 

Du Toits Pan Mines, 1, 20 

1885, section, 3 
Dumas, J. B., 41 



INDEX 



71 



Damour, A. A., 44 

Dunite, 49 

Dunn, E. J., 3, 6, 52 



Elliott Co. (Ky.), Kimberlite, 56, 58, 

61, 65, 66 

Enclosures, fragmentary, 45 

4 Eozoonal ' structure, 18 

Epidote, 37 

Estherville meteorite, 54 

Euganeaa Hills (Italy) breccia, 55 

Euphotide, 4 

4 Eye-gneiss,' 53 



Kentucky, Kimberlite, 56, 61, 65, 66 

— peridotite, 35 
Kimberley (S. Africa) Mines, 1 

— diamonds, 43 
Kimberlite, 50 

— analysis, 01 

— composition of, 62 

— Kentucky, 56, 61 

— New York State, 56, 5$ 
Kjerulf, T., 49, 53 
Klein, J. F. C, 32 
Knop, A., 37, 41 
Koksharow, N. von, 32 
Kunz, G. F., 40 



Fizeau, A. H. L., 43 
Flight, W., 5, 20, 27, 52 
Fouque, F., 41 



Gabbro, decomposed, 4 
Garnet, 28 
Gibbsite, 45 
Griesbach, C. L., 7 
Griqua Land mines, 2 
Groth, P., 32 
Ground-mass, 45 
— chemical composition, 40 



Hatdinoer, W. von, 57 
Halting, P., 43 
Hawes, G. \V., 43 
Hedley, T., 7, 42 
Herwig, F., 22 
Hudleston, W. H., 7, 52 
Hunt, T. S., 58 
Hussak, E., 18, 34 



Igneous lava, matrix a true, 52 
Ilmenite, 37 
Inclusions, diamond, 43 



Jannettaz, E., 43 
Jeremejew, P. von, 40 
Jones, T. R., 4, 7, 9 
Judd, J. W., 27 



Kalkousky, E., 26 
Karoo beds, 7 
— (Upper) plateau, 2 
Kenngott, G. A., 43 



Lava, porphyritic, 51 
Lemberg, J., 49 

Levy, A. Michel-; see Michel-Levy, A. 
Lewis, H. Carvill, on ' Matrix of the 
Diamond,' 10, 68 
- collection of rocks, oS, 04 
Limburgite, 55 
Losch, A., 29 



Magnetite, 36 

Maskelyne, N. 8., 5, 20, 27, 52 

Matrix, diamond, 10, 44 

— minerals, 11 
Melilite, 49 
Meteorites, 54, 57 
Mica, 25 

— analysis, 28 
Michel-Levy, A., 23, 41 
' Mimetic minerals,' 32 
Minerals, diamond, 11 

— matrix, 44 

4 Mortel-structur,' 53 
Moulle, A., 40, 52 



Naumann, C. F., 54 

4 Nephelin-pikrit,' 34 

New York State, Kimberlite, 50, oS 

— peridotite, 35 



Octaiielrite. 62 
Olivine, 0, 12, 17 

— surrounded by perovskite, 34 
« Olivinfels,' 40 ' 
Ophicalcite, 48 

Orange Free State Klines, 2 

— River diggings, 1 
Orthite, 37 




72 



INDEX 



Peridotite, 17, 42, 68 

— analyses, 64 

Perovskite, 29, 31, 32, 33, 34, 36 

Petzhold, A., 44 

Picotite, 36 

Picrite-porphyrite, 50 

4 Pipes,' volcanic, 4 

Pleistocene depression, 38 

Porphyritic lava, 51 

Pyroxenic minerals, 19 



Quartz, liquid carbonic acid in, 43 



Eammelsberg, C. F., 28, 48 

Eath, G. Vom, see Vom Hath 

Beunert, T., 40 

Eeusch, H. H., 53 

Eeyer, E., 55 

Eoot, 0., 60 

Eoscoe, Sir H. E., 51 

Eosenbusch, H., 9, 18, 23, 26, 49, 58 

Eoth, J., 54 

Eussian diamonds, 29 

Eutile, 16 



Sandstone in volcanic ' pipes,' 4 

Saude, Ben, 32 

Sauer, A., 33, 34 

Schrauf, A., 23 

Serpentine, 7, 12, 21, 38, 68 

— analysis, 61 

Shale fragments surrounded by cal- 

cite, 46 
Shale in volcanic ' pipes,' 4 
Shaw, J., 3, 9 
Sjogren, 37 

Smaragdite, analvsis, 19 
Sorby, H. C, 44 ' 
Sphene, 38 

Stelzner, A., 34, 48, 49 
Stone, Sir J. B., 45, 69 



Stow, G. W., 3, 7 

Syracuse (N.Y.), Kimberlite, 56, 58 

Syssersk (Urals), 29 



Talc, 38 

Titanic iron in perovskite, 33 

Titaniferous magnetite, 36 

Tornebohm, A. E., 23, 37, 49 

Tourmaline, 38 

' Trapp-eisenerz,' 36 

Tremolite, 14, 38 

Triassic (post-) age of diamond, 7, 10 

Tschermak, G., 20, 22, 32, 49, 50, 57 



United States, Kimberlite, 56, 58 
Urot Mines, 2 



Vaal Eiver diggings, 1 

— dykes, 9 
Vaalite, 5, 28 

— analysis, 28 
Vanuxem, L., 58 

Volcanic intrusions in Karoo beds, 7 
Volcanic ' pipes,' 4 
Vom Eath, G., 22, 37 



Wadsworth, M. E., 23, 53, 54 

Wales, volcanic breccia in, 55 

Wiik, F. J., 22 

Williams, G. H., 26, 35, 58, 60 

Wobler, F., 44 

Wright, A. W., 43 



Yellow ground/ 3, 62 



Zeolites, 39 

Zirkel, F., 13, 26, 27, 33, 43 



PRINTED BY 
SFOTTISWOODK AND CO., NEW-STREET SQUARE 

LONDON 



PLATE II.— Microscopic Sections of Kimberlite. 




(i) THE KIMBERLEY ROCK. 




f 



(2) THE NORTH AMERICAN ROCK. 



The Graphotone Co., Art Printers, Push Hill Park, Enfield. 




QES. 



•*• ' iitiiK 



ECTATO* A l\ 



The fol -sting letter from the Duke of Fife appears in the 

Spectator of r ' -> lo tice in the Spectator of May 15 the following 
comment on / . jnce before the South Africa Committee : M It 
nevertheless r nai.. most astonishing fact that the Duke of Fife can 
retain his regai 1 for a man who treated him like a clerk, and, as he says, 
deceived him. hat shows a meeker spirit than one would expect to find 
even in a newly-h>dged curate." Had this remark appeared in any other 
newspaper, I should have treated it with the contempt it deserves ; but, 
having been a consistent reader for twenty years of your paper, and 
admired its high tone and general fairness, I cannot refrain from writing 
you thefollowingwords in reply. It might have occurred even to a " newly- 
fledged "journalist that it is possible for a man to continue to have a regard 
for another who has deceived him, if he is convinced that that man had no 
sordid motive for his conduct, but ffas actuated by a sincere desire to 
promote the highest interests of his country. I am aware that this is 
not the view which the Spectator takes of Mr. Rhodes's conduct, but as 
it happens to be mine, I should make the same declaration again if a 
similar occasion arose. — I am, Sir, &c., Fife. 

Upon which the Editor of the Spectator comments thus: "The 
Duke of Fife's reply was anticipated by Walter Savage Landor : 

1 You smiled, you spoke, and I believed, 
By every word and smile deceived. 
Another man would hope no more, 
Nor hope I what I hoped before ; 
But let not this last wish be vain — 
Deceive, deceive me once again ! ' " 

One wonders whether his Grace will " make the same declaration 
again " in relation to the Spectator itself. 



OPENING OF BLACKWALL TUNNEL. 




FORECAST OF TO-DAY'S CEREMONY. 



O-DAY sees the opening of the Black* 
wall Tunnel by the Prince of Wales. 
We have from time to time — and so 
lately as last evening — published so 
many details as to the construction of 
this magnificent engineering work, 
that there is really nothing to add, 
except to give brief details of to-day's 
ceremony. The Prince will be accom- 
panied by the Princess of Wales, 
Princess Victoria, and the Duke of 
York, and the party will leave Marl- 
borough House for Blackwall at 2.40 
this afternoon, attended by the great officers of her Majesty's Household 
and the Household in Waiting. The processsion will consist of four 
carriages and a captain's escort of the 1st Life Guards. The 
route taken will be by Pall-mall, Cockspur-street, Northumberland- 
avenue, Victoria Embankment, Queen Victoria-street, Comhiil, Leaden- 
hall-street, Aldgate High-Street, Whitechapel High-street, Commercial- 
road, East, East India Dock-road, to the northern approach of the tunnel. 
Here the procession will be met by Dr. Collins, chairman of the council, 
Mr. R. M. Beachcroft, vice-chairman, Mr. A. M. Torrance, deputy-chair- 
man, Mr. W. Bull, chairman, and the other members of the Bridges 
Committee. The Prince of Wales will then be presented with a gold 
key, and Dr. Collins will, at his Royal Highness's desire, unlock the 
gates. ^ Their Royal Highnesses, who will here be joined by the Duke of 
Cambridge and the Duke of Teck, will proceed through the tunnel to 
the southern approach to a pavilion, where the Prince of Wales will, in 
the Queen's name, declare the tunnel open to the public for ever. After 
the ceremony the Royal party will return by way of Blackwall-lane t 
Trafalgar-road, Romney-road, London-street, Greenwich-road, Deptford- 
bridge, Deptford-broadway, New Cross-road, Old Kent-road, New 
Kent-road, St. George's-road, Westminster Bridge-road, Bridge-street, 
Parliament-street, Whitehall, Charing Cross, Cockspur-street f and 
Pall Mall. 



THE QUEEN'S VISIT TO SHEFFIELD. 

STRIKING SCENE AT MESSRS. CAMMELL'S. 

The Queen's visit to Sheffield yesterdav was a great success in ever 



"THE GENESIS AND MATRIX O THE DIAMOND." 

Professor 1\ G. Bonney has edited, and Messrs. Longman have pub- 
lished, some « Papers and Notes on the Genesis and Matrix of the 
Diamond," by the late Professor H. C Lewis, of Philadelphia and 
Harvard. The subject is a peculiarly interesting one, but the Professor's 
papers are rather technical, and, on the whole, appeal more to the 
geologist than to the ordinary reader. Some particulars given, how- 
ever, will be read by everybody. It is largely the South African 
diamond fields to which the papers refer. 

The First South African Diamonds. 

The first diamond was found in South Africa just thirty years ago, 
when a large specimen was picked out of a lot of rolled pebbles gathered 
in the Orange River. This led to the river diggings in the Orange and 
Vaal rivers : 

, In 1870, when perhaps 10,000 persons had gathered along the banks of the Vaal 
River, the news came of the discovery of diamonds at a point some fifteen miles away 
from the river, where the town of Kimberley now stands. These were the so-called 
'dry diggings/' which at first were thought to be alluvial deposits, but have proved 
to be volcanic pipes of a highly interesting; character. In 1871 four mines were dis- 
covered in close proximity to Kimberley, all of which have since become famous, 
They are known as Du Toit's Pan, De Beers, Kimberley, and Bulfontein Mines 
all of which could be enclosed by a circle three and a half miles in diameter. 

The mines lie at the northern end of a great plateau which" extends 
from the Bokkeveldt Mountains, at the Cape of Good Hope, to the 
border of the Transvaal Republic. 

Six Tons of Diamonds. 

Other mines were soon being worked in the neighbouring territory, 
but none of them have equalled in richness the four great mines first 
discovered. "These four all have the same geological structure, 
each being a separate pipe ; and all are remarkably rich in diamonds! 
It has been estimated that since the opening of "these mines (up to 
1886) more than six tons of diamonds have been extracted from them, 
being probably greater than the total combined previous production of 
all the other mines in the world." The quantity since must have been 
very much more. 

The Diamond Bearing Material. 

On this subject Professor Lewis says : 

The diamond bearing material first excavated was a soft yellowish friable sub- 
stance readily crumbling when exposed At the depth of about 100 feet it became 
darker and harder, and finally acquired a slate blue or dark green colour, resembling 
some varieties of serpentine. This is the well-known "blue earth " of the diamond 
mines, which proved to be richer in diamonds than the wholly decomposed and 
weathered portion first penetrated, and called "yellow ground." This " blue earth : ' 
or "blue ground "is taken out of the mine and exposed to trje.s^u%and it is then 
capable of being readily crushed and washed for the extraction of its included 
diamonds. The " blue ground " is greasy to the touch like serpentine, and is mil of 
enclosed fragments of sbte and other substances. 

The deepest sinkings in Kimberley mine ten years ago were six 
hundred feet below the surface. They are now nearly three times 
that depth. 

The M&trix. 
The conditions under which diamonds occur in South Africa are 
said to be quite different from those of every other known locality. 
These conditions have been often described, but, as we have said, the 
subject is a rather technical one. Here, however, is one extract from 
Professor Lewis's paper on the subject : 

Mr. ITuddleston holds that' the matrix of the diamond was a sort of volcanic 
breccia which was made hydrous at a considerable depth, and ejected in a wet state 
accompanied by steam, like the product of a mud volcano. The earlier theories as to 
the origin of the diamond have, in the light of new facts, quite given wav to the 
theory that the diamonds belong to and are part of the matrix in which they lie, 
and that this matrix is in some way of volcanic origin either in the form of mud or 
ashes or lava. 

The diamond-bearing pipes penetrate strata of Triassic age which 
are known as the Karoo beds. 

The De Beers Mine To-Day. 

Professor Lewis proceeds at considerable length to describe the 
diamond-bearing rock— the minerals of which it is composed, its 
chemical composition, its structure, and its geological characters' and 
significance. There is also a section describing Kimberlite from the 
United States. Into these matters, of course, we cannot go; but the 
following extract from a note by Professor Bonney at the end of the 
book may be given : 

1 , m cL a r' d that in 1896 the workin S s in the De Beers Mine had reached a depth of 

over 1,500 feet. They have ceased to work the diamond-bearing roek by excavating 

it vertically downwards from the top of the "pipe," but sink shafts through the 

country rock ' (shale, quartzite, and melaphyre), from which they drive levels into 

the pipe itself, removing its contents by means of these, as it were layer by layer. 

While the last sheets of the book were in the press Sir J. B. Stone, J 
M.P., sent Professor Bonney a collection of specimens which he had] 
recently received from the De Beers Mine, among which were pieces of I 
the diamond-bearing rock, of which the deepest was labelled 1,400ft. I 
The shaft of the mine has reached a depth of quite 1,500ft., and fronj 
it the lowest level is beinsr driven. I 



My post-office address is 
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My express address is 



DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY 




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THE GENESIS OF THE DIAMOND. 

There has recently been published a volume 
of small size, but of especial interest and im- 
portance, in regard to the origin of diamonds. 

This is none other than the posthumous issue 
of the full papers of the late Professor H. Car- 
vill Lewis, edited by his friend, Professor T, G. 
Bonney, of London.* 

* Papers and notes on the ' Genesis and Matrix of 
the Diamond.' By the late Henry Carvill Lewis, 
M.A., F.G.S., Professor of Mineralogy in the Acad- 
emy of Natural Sciences, Philadelphia, Professor of 
Geology in Haverford College, U. S. A. Pages xvi-f 
72. 2 Plates. Edited from his unpublished MSS., 
by Professor T. G. Bonney, D.Sc. LL.D., F.R.S., &c. 
Longmans, Green & Co. , London and Bombay. 1897. 
It will be remembered that Professor Lewis 
was the first to present a clear and definite theory 
of the origin of the South African diamonds, as 
resulting from the intrusion of igneous rocks into 
and through carbonaceous shales, and the crys- 
tallization of the carbon throughout the rock as 
it cooled, from hydrocarbons distilled from the 
shale that had been broken through. These 
views, now for the most part accepted, and sub- 
sequently confirmed by other and very interest- 
ing parallel discoveries, he presented in two 
papers read before the British Association for 
the Advancement of Science at its meetings held 
in 1886, at Birmingham, and in 1887, at Man- 
chester. Before he was able, however, to pre- 
pare them for publicatior and carry them to the 
greater completeness that he desired, Professor 
Lewis succumbed to an attack of typhoid fever, 
which removed one of the most brilliant and 
capable of the rising scientists of this country. 
Agreeably to his expressed wishes, his material 
was entrusted to his friend and co-laborer, Pro- 
fessor George H. Williams, of Johns Hopkins 
University; but, by a strange fatality, before 
the latter had time to arrange and edit these 
papers this distinguished scientist also fell a vic- 
tim to the same disease, in 1894. The work was 
then committed to Professor Bonney and is at 
last given to the scientific world. 

The book consists of an introductory note by 
Mrs. Lewis ; a preface by Professor Bonney ; the 
two papers of Professor Lewis himself, with 
some later notices and references by the editor • 
a brief account of similar material from other 
localities, belonging to Professor Lewis — also by 
the editor ; a closing note on some other MSS. 
of Professor Lewis, and a full index. There 
are also two plates and a number of smaller il- 
lustrations, the latter from Professor Lewis' own 
drawings. 

The first paper, ■ On a diamond-bearing peri- 
idotite and on the history of the diamond ' (1886), 
is brief, dealing with the general character and 
occurrence of the diamantiferous rock at Kim- 
berley, and outlining Professor Lewis' theory. 
The second paper, 'The matrix of the 
diamond ' (1887), is more extended and goes 
into an exhaustive discussion and comparison of 
the various aspects, contents and alterations of 
the rock, which he finds to be different from 
any previously descried, and. tW*fn™ „™. 



some later notices and references by the editor ; 
a brief account of similar material from other 
localities, belonging to Professor Lewis— also by 
the editor ; a closing note on some other MSS. 
of Professor Lewis, and a full index. There 
are also two plates and a number of smaller il- 
lustrations, the latter from Professor Lewis' own 
drawings. 

The first paper, < On a diamond-bearing peri- 
dotite and on the history of the diamond ' (1886), 
is brief, dealing with the general character and 
occurrence of the diamantiferous rock at Kim- 
berley, and outlining Professor Lewis' theory. 
The second paper, 'The matrix of the 
diamond ' (1887), is more extended and goes 
into an exhaustive discussion and comparison of 
the various aspects, contents and alterations of 
the rock, which he finds to be different from 
any previously described, and, therefore, pro- 
poses for it the name of Kimberlite. Its main 
character is that of a highly basic porphyritic 
peridotite, filled with olivine crystals and 
grains, more or less altered, and various other 
minerals— serpentine, tremolite, etc. , with 
bronzite, rutile, perovskite, pyrope garnets, 
micaceous minerals and other forms, and at 
times brecciated in structure, filled with frag- 
ments of carbonaceous shale brought up from 
below. The shales are of Triassic age, the 
1 Karoo beds ' of that region, and the intrusion 
of the peridotite in the great < pipes ' or chim- 
neys that constitute the mines is therefore 
proved to be of a later, though not exactly de- 
termined period. 

The question has sometimes been raised 
whether the diamonds themselves may not have 
been carried up from a deeper source in rocks 
below, instead of originating in the peridotite ; 
and the occurrence of broken crystals has been 
cited in support of this view. Professor Lewis, 
however, disposes very completely of this idea 
in two ways : He refers to the well-known fact 
that each of the great mines or < pipes ' yields 
diamonds that have, in some respects, a type of 
character peculiar to that one and different from 
the others, so that African exports, and even 
those who have never been there, can recognize 
from which mine any diamond has come. 
Further, as to the broken crystals, he shows 
that breakage not unfrequently occurs after the 
diamonds are removed from the rock, and 
points out that this is a result of strain in their 
formation, as indicated by microscopical and 
optical examination, and that such a condition 
is known to produce ruptures and explosions in 
other minerals. It may be added here, al- 
though Professor Lewis does not speak of it; 
that many crystals must be broken in the blast- 
trig of the rock, the shoveling and the carting 
of the loosened material, and the various me- 
chanical processes employed at the mines, and 
that pieces of such broken crystals would be 1 
separated and scattered to various parts of the 
immense dumping and weathering floors, never 
to be recognized as fragments of the same one 
when finally recovered, perhaps at very differ- 
ent times. 

The rock itself is a dark green, compact ma- 
terial, resembling serpentine and containing a 
large proportion of olivine, in grains and crys-' 
tals ; several green minerals that are not con- 
spicuous, from the resemblance of their color 
to the ground-mass (enstatite, chrome-diop- 
side, smaragdite and bastite); arnica, probably 
biotite, more conspicuous and quite abundant, 
and frequent grain, of nvrn., * M ^.1 



■^^ 



neys that constitute the mines is therefore 
proved to be of a later, though not exactly de- 
termined period. 

The question has sometimes been raised 
whether the diamonds themselves may not have 
been carried up from a deeper source in rocks 
below, instead of originating in the peridotite ; 
and the occurrence of broken crystals has been 
cited in support of this view. Professor Lewis, 
however, disposes very completely of this idea 
in two ways : He refers to the well-known fact 
that each of the great mines or * pipes ' yields 
diamonds that have, in some respects, a type of 
character peculiar to that one and different from 
the others, so that African experts, and even 
those who have never been there, can recognize 
from which mine any diamond has come. 
Further, as to the broken crystals, he shows 
that breakage not unfrequently occurs after the 
diamonds are removed from the rock, and 
points out that this is a result of strain in their 
formation, as indicated by microscopical and 
optical examination, and that such a condition 
is known to produce ruptures and explosions in 
other minerals. It may be added here, al- 
though Professor Lewis does not speak of it, 
that many crystals must be broken in the blast- 
ing of the rock, the shoveling and the carting 
of the loosened material, and the various me- 
chanical processes employed at the mines, and 
that pieces of such broken crystals would be 
separated and scattered to various parts of the 
immense dumping and weathering floors, never 
to be recognized as fragments of the same one 
when finally recovered, perhaps at very differ- 
ent times. 

The rock itself is a dark green, compact ma- 
terial, resembling serpen ine and containing a 
large proportion of olivine, in grains and crys- 
tals ; several green minerals that are not con- 
spicuous, from the resemblance of their color 
to the ground-mass (enstatite, chrome-diop- 
side, smaragdite and bastite); a mica, probably 
biotite, more conspicuous and quite abundant, 
and frequent grains of pyrope garnet, sometimes 
of gem quality and great beauty, and miscalled 
1 Cape Rubies. ' Of smaller disseminated min- 
erals are to be noted perovskite, quite frequent, 
and magnetite, chromite, ilmenite and picotite,' 
less so, though common. Rare and minute oc- 
currences are apatite, epidote,orthite, tremolite, 
tourmaline, rutile, sphene, leucoxene. As de- 
composition products there are serpentine and 
calcite, abundant, and zeolites, chalcedony and 
talc ; also cyanite (?) These, with the dia- 
monds and the included fragments of carbona- 
ceous shale, make up the contents of this re- 
markable rock. 

Professor Lewis then goes into a detailed 
account of the mode of occurrence of these 
minerals, beginning with the most conspicuous 



I^ » tf — — fcWMJW— * 



^P S W ^ '-^?' 1 



Sci 8 E 

species — the olivine — which is remarkable for 
its fine cleavage-surfaces and very interesting 
in its alterations. These are chiefly (1) into 
serpentine, proceeding from without inward, 
and penetrating along crevices and fractures, 
also sometimes in the form of chrysotile, pro- 
ducing a velvety border or coating to the grain; 
(2) tremolite, more internal, the fibrous struc- 
ture developing parallel to the vertical axis 
and domes of the olivine crystals ; (3) when 
both these alterations are present and have 
gone so far as to obliterate most or all of the 
olivine, a talc-like substance intervenes be- 
tween them in which are developed minute 
needles of rutile, arranged parallel to the faces 
of the olivine crystal. The rock contains every 
stage of these changes from pure bright unal- 
tered olivine to those forms that have borders 
of serpentine or chrysotile, or incipient tremo- 
lite fibers within, to the complete alteration 
just described. The relation of all these to 
similar phenomena in other rocks, and in 
meteorites, is discussed with much fulness. 

Professor Lewis then takes up the smarag- 
dite, chrome-diopside, bastite and enstatite (or 
bronzite, for it is just on the line between the 
two varieties). The two first named are, in 
some cases, fine enough in color and clearness 
to yield gems, and also sometimes the bron- 
zite ; all are colored by chromium. The diop- 
side occasionally gives rise to calcite by alter- 
ation. 

The mica is next considered ; as all who are 
familiar with the rock are aware, it is the most 
prominent of the contained minerals to the eye. 
It is somewhat anomalous in character, being 
chemically a biotite, but optically nearer to 
phlogopite. It occurs in several distinct ways: 

(1) as included crystalline masses or plates, 
apparently an original ingredient of the rock ; 

(2) surrounding grains of pyrope ; (3) rarely, 
as a result of the alteration of enstatite ; and 
(4) as a metam orphic \ product from the included 
fragments of shale; and the first form has pro- 
duced, by hydration, the vermiculite variety 
called vaalite, which occurs freely in the de- 
composed peridotite so largely known as the 
i blue-ground. ' 

After referring to the pyrope garnets, and 
suggesting that the various garnetiferous ser- 
pentines are doubtless derived from the decom- 
position of similar peridotites, as further indi- 
cated by their likewise containing olivine, bron- 
zite, chrome-diopside, etc., he mentions another 
variety of garnets as found in this rock, very 
small, very brilliant, very hard, colorless or 
greenish, and extremely difficult to distinguish 
from small diamonds. These Professor Lewis 
is inclined to refer to demantoid. (?) 

An interesting part of this discussion next 
follows, in relation to the perovskite, which is 
pretty abundant in small crystals, of cubical 
habit. Professor Lewis gives much attention, 
and a number of drawings, to the optical fea- 
tures of this species, and strongly inclines to 
the view that regards perovskite as a highly 
twinned orthorhombic mineral and not isomet- 
ric save in external aspect. This has long been 
a mooted point, and these observations are an 



M^MMMfeMU^MMMMaiaiiMMlB 



*__ 



^ 



~z ite, curunreHAiupsiue, etc., ne i i renti i niB auumci - 
variety of garnets as found in this rock, very 
small, very brilliant, very hard, colorless or 
greenish, and extremely difficult to distinguish 
from small diamonds. These Professor Lewis 
is inclined to refer to demantoid. (?) 

An interesting part of this discussion next 
follows, in relation to the perovskite, which is 
pretty abundant in small crystals, of cubical 
habit. Professor Lewis gives much attention, 
and a number of drawings, to the optical fea- 
tures of this species, and strongly inclines to 
the view that regards perovskite as a highly 
twinned orthorhombic mineral and not isomet- 
ric save in external aspect. This has long been 
a mooted point, and these observations are an 
important contribution. Of much interest also 
are the chemical and genetic relations of this 
species as here presented ; the crystals often 
enclose grains of what Professor Lewis terms a 
titanic spinellid, perhaps a tjtaniferous magne- 
tite, perhaps ilmenite, indicating a derivation 
therefrom ; they also, in some cases, lie in a 
curious manner, upon or around partially al- 
tered olivine crystals. The remark is made 
that, while perovskite is familiar in various 
non-feldspathic igneous rocks, it has not been 
found in peridotite until Professor Williams 
recognized it in the peculiar rock from Syra- 
cuse, N. Y., and that later Professor Lewis 
!4§ntified it in the similar rock from Isom's 
Creek, Kentucky, where it had been previously 
regarded as anatase. These three rocks, those 
just named and the African, are the only known 
occurrences of what is here named Kimberlite. 
The article goes on to show that in basic 
eruptive rocks the titanium takes the form 
of perovskite, while in acid rocks it forms 
sphene ; in intermediate ones it develops 
ilm,enite or titanic iron ; and these deductions 
harmonize precisely with important experi- 
ments of Bourgeois, in the artificial produc- 
tion of titanium minerals. 

After going into some particulars as to the 
minor minerals found in this rock, Professor 
Lewis then takes up the base or ground mass 
and discusses it minutely. He terms it 'a 
mpre or less homogeneous serpentinous mass,' 
very difficult to study by reason of its decom- 
posed condition, consisting now of a mixture of 
serpentine with calcite and some other pro- 
ducts of alteration, the original structure being 
wholly lost. 

Fragmental enclosures are frequent, 'both 

of the adjoining shale and diabase, and also of 

more deeply seated granite, gneiss, eclogite, 

and other related rocks. ' Of these the shale 

predominates, sometimes making the rock" a 

oreccia. The shale itself is highly charged with 

carbon, so as to be quite combustible ; but the 

included fragments are altered, having lost their 

carbon and become harder, sometimes even 

metamorphosed to a micaceous structure, as 

before referred to. In size they vary from 

large masses, in the upper part of the mines, 

called by the workers bloating-reef,' to small 

fragments, diminishing in number and size in 
descending. 

P»rofessor Lewis goes into very detailed petro- 
graphical and chemical discussion as to the 
original character of the rock, in which it is 
Jiardly possible to follow him in a review, and 
finding no known rock that presents identical 
characters, he proposes for it the name of 
Kimberlite. This he designates as ' a porphy- 
ritic volcanic peridotite of basaltic structure. ' 



recognized it in the peculiar rock from Syra- 
cuse, N. Y., and that later Professor Lewis 
i4fentified it in the similar rock from Isom's 
Creek, Kentucky, where it had been previously 
regarded as anatase. These three rocks, those 
just named and the African, are the only known 
occurrences of what is here named Kimberlite. 
The article goes on to show that in basic 
eruptive rocks the titanium takes the form 
of perovskite, while in acid rocks it forms 
sphene ; in intermediate ones it develops 
ilm.enite or titanic iron ; and these deductions 
harmonize precisely with important experi- 
ments of Bourgeois, in the artificial produc- 
tion of titanium minerals. 

After going into some particulars as to the 
minor minerals found in this rock, Professor 
Lewis then takes up the base or ground mass 
and discusses it minutely. He terms it ' a 
mpre or less homogeneous serpentinous mass,' 
very difficult to study by reason of its decom- 
posed condition, consisting now of a mixture of 
serpentine with calcite and some other pro- 
ducts of alteration, the original structure being 
wholly lost. 

Fragmental enclosures are frequent, 'both 
of the adjoining shale and diabase, and also of 
more deeply seated granite, gneiss, eclogite, 
and other related rocks.' Of these the shale 
predominates, sometimes making the rock a 
breccia. The shale itself is highly charged with 
carbon, so as to be quite combustible ; but the 
included fragments are altered, having lost their 
carbon and become harder, sometimes even 
metamorphosed to a micaceous structure, as 
before referred to. In size they vary from 
large masses, in the upper part of the mines, 
called by the workers * floating-reef, ' to small 
fragments, diminishing in number and size in 
descending. 

Erofessor Lewis goes into very detailed petro- 
graphical and chemical discussion as to the 
original character of the rock, in which it is 
Jjardly possible to follow him in a review, and 
finding no known rock that presents identical 
characters, he proj>oses for it the name of 
Kimberlite. This he designates as ' a porphy- 
ritic volcanic peridotite of basaltic structure,' 
and notes three forms of its occurrence : (1) 
Kimberlite proper, a typical porphyritic lava ; 
(2) Kimberlite breccia, the same rock broken 
and crushed by volcanic movements and 
crowded with included fragments of shale ; (3) 
Kimberlite tuff, the fragmental and tufaceous 
portion of the same rock. These varieties 
graduate into each other, and all occur together 
in the same neck or crater, the second, how- 
ever, being most abundant and most productive 
of diamonds. 

He treats of the origin of the brecciated 
structure, which has caused much discussion, 
some geologists regarding the whole rock as a 
sort of tufa or volcanic mud, while others hold 



^p 



soi 9 E 

that it is a true outpouring lava that has car- 
ried up fragments of the rocks broken through 
it its course, and has since been largely decom- 
posed. Professor Lewis urges the latter theory 
strongly, and supports it by many arguments ; 
while the editor, Professor Bonney, evidently 
inclines to the other view, advocated by Pro- 
fessor W. H. Hudleston, in 1885, and by 
some others. There is not space here to review 
Professor Lewis' several arguments for the true 
igneous character of the Kimberlite and against 
the tufaceous theory. The one to which Pro- 
fessor Bonney accords the chief importance is 
the identity of the rock with that from Syra- 
cuse, New York, and Elliott county, Kentucky, 
where it occurs in actual dikes, such as are not 
found in tufas. The brecciated character, 
which is so marked, is referred by Professor 
Lewis to three causes, acting either separately 
or perhaps together. These are (1) rapid cool- 
ing and shrinkage; (2) i friction brecciation,' 
from contact with the wall-rock ; and (3) sub- 
sequent movements and explosions in the crater 
itself, below. He illustrates and parallels the 
first of these from meteorites, to some of which 
this rock bears marked resemblance both in 
structure and contents, and the others from 
well-known occurrences in terrestrial volcanic 
rocks. 

The third section of the volume is occupied 
with a detailed account, from specimens and 
notes of Professor Lewis, of the two other 
known occurrences of Kimberlite, at Syracuse, 
N. Y., and Willard, Ky. The identity of these 
with the African rock, in almost all particulars, 
is remarkable, and as they form definite eruptive 
dikes, Professor Lewis' view as to the latter is 
strongly confirmed. 

It remains only to call attention to other and 
later facts which tend to bear out the views pre- 
sented in this remarkable posthumous article. 

The presence of a residual hydrocarbon in the 
rock of the African diamond mines was shown 
by an interesting and important observation of 
Sir Henry E. Roscoe (Proc. Lit. and Phil. Soc. 
of Manchester, XXIV., 1885, p. 5), which is al- 
luded to by Professor Lewis in his second paper, 
and has frequently been cited in discussions of 
the subject. He found that the 'blue-ground ' 
on treatment with hot water yielded an aro- 
matic hydrocarbon, which he was able to sepa- 
rate by digesting the l blue-ground ' with ether 
and evaporating the solution. It then appeared 
as a crystalline aromatic solid, burning with a 
smoky flame (showing it rich in carbon), volatile, 
and melting at 50° C. 

The bearing of this fact upon Professor Lewis' 
theory is clear. It indicates that the igneous 
rock, breaking through the highly carbonaceous 
Karoo shales (37.50 p. c. of carbon ; Whitfield, 
U. S. Geological Survey ; Gems and Prec. Stones 
North America, 1889, p. 33) became charged 
with volatilized hydrocarbons distilled from the 
shale, and that in cooling these had crystallized 
partly into diamonds and partly into the many 



W1WRJ BflSm (yiMVIug il ncL in carbon), volatile, 
and melting at 50° C. 



' i - 



r Pll a hnnu'v.™ ^x-P J.1- 



u 



theory is clear. It indicates that the igneous 
rock, breaking through the highly carbonaceous 
Karoo shales (37.50 p. c. of carbon ; Whitfield, 
U. S. Geological Survey ; Gems and Prec. Stones 
North America, 1889, p. 33) became charged 
with volatilized hydrocarbons distilled from the 
shale, and that in cooling these had crystallized 
partly into diamonds and partly into the many 
carbonadoes, larger and smaller, which are dis- 
tributed through the rock. Professor Roscoe's 
material strongly suggests this theory, which, 
indeed, he himself independently propounded. 
In 1886 a meteorite fell at Novo Urei (Sep- 
tember 22d) in the province of Pensa, Russia, 
which was found to contain about 1 per cent, of 
diamond carbon, in the form of gray parti- 
cles.* 

*Daubree's discussion of the analogy of the occur- 
rence of the diamond in the meteorites and in the 
South African Kimberlite was the next important 
paper on this subject. (Comptes Eendus, 110-18, 
1890. ) 

In 1887 Mr. Fletcher (Miner alogical Magazine. 
7, 121) described the new mineral ' Cliftonite ' 
— a black substance with a hardness of 2.5 and 
a density of 2.12, occurring in cubes with faces 
Of the dodecahedron or tetrahexahedron in the 
meteorite of Youndegin, West Australia. This 
suggested a graphitic alteration of diamond— a 
view taken by Brezina (Ann. Mus. Wien, IV., 
102, 1889) regarding this new species and cer- 
tain graphitie crystals of cubic type, observed 
long before in the Arva meteorite and regarded 
as pseudomorphs after pyrite by Haidinger 
(Pogg., 67, 437, 1846), but later by Rose, as after 
diamond (Beschr. Meteor., 40, 1864). Similar 
crystals were also known in the Sevier iron of 
Cocke county, Tenn. 

In 1891 the discovery of diamond, or at least 
of diamond carbon, in some quantity in the 
meteoric iron of Canon Diablo, Arizona, was 
announced by the late Professor A. E. Foote 
(Amer. Jour. Science, Vol. XLIL, July, 1891, pp. 
413-417) and Dr. George A. Koenig. In July, 
1892 (Science, p. 15), Dr. O. W. Huntington 
gave further experiments on the same material, 
confirming the decisions of Professors Foote and 
Koenig; and in December of the same year 
similar results were published by M. C. Friedel 
(Bulletin de la Soc. Francaise de Mineralogie, No. 
9, p. 258). A crucial test was then proposed 
by G. F. Kunz, of New York, and carried out 
in the presence of Dr. Huntington, at the 
World's Fair at Chicago, September 11, 1893, 
viz., the cutting of polished faces on pieces of 
diamond with some of the carbon powder from 
the cavities of the Canon Diablo meteorite 
(Amer. Jour. Scl, Vol. XLVL, December, 1893; 
and Min. Resources U. S., 1893, pp. 683-685). 
In the meantime Professor Henri Moissan, 
of Paris, had been making his now celebrated 
experiments on the artificial production of 
diamonds from the cooling, under extreme 
pressure, of highly carbonated iron fused in a 
specially constructed electric furnace (Mineral 
Resources U. S., 1895, pp. 903-904). 

All these facts taken together form a remark- 
able series of confirmatory evidence of the 
views advocated by our late countryman in re- 
gard to the production of this most precious of 
gems, the origin of which has been so obscure a 
problem in mineralogy and geology. Another 

Point 0fm'ort lR Pl P ntifin1nfnv,„< .1, ,-..1 i :- y 



"— - — ■— 



"' "—*"■"■ ' 



1890. ) 

In 1887 Mr. Fletcher (Mineralogical Magazine, 
7, 121) described the new mineral ' Cliftonite ' 
— a black substance with a hardness of 2.5 and 
a density of 2. 12, occurring in cubes with faces 
of the dodecahedron or tetrahexahedron in the 
meteorite of Youndegin, West Australia. This 
suggested a graphitic alteration of diamond — a 
view taken by Brezina {Ann. Mus. Wien, IV., 
102, 1889) regarding this new species and cer- 
tain graphitie crystals of cubic type, observed 
long before in the Arva meteorite and regarded 
as pseudomorphs after pyrite by Haidinger 
(Pogg., 67, 437, 1846), but later by Rose, as after 
diamond (Beschr. Meteor., 40, 1864). Similar 
crystals were also known in the Sevier iron of 
Cocke county, Tenn. 

In 1891 the dkcovery of diamond, or at least 
of diamond carbon, in some quantity in the 
meteoric iron of Canon Diablo, Arizona, was 
announced by the late Professor A. E. Foote 
(Amer. Jour. Science, Vol. XLIL, July, 1891, pp. 
413-417) and Dr. George A. Koenig. In July, 
1892 (Science, p. 15), Dr. O. W. Huntington 
gave further experiments on the same material, 
confirming the decisions of Professors Foote and 
Koenig ; and in December of the same year 
similar results were published by M. C. Friedel 
(Bulletin de la Soc. Francaise de Mineralogie, No. 
9, p. 258). A crucial test was then proposed 
by G. F. Kunz, of New York, and carried out 
in the presence of Dr. Huntington, at the 
World's Fair at Chicago, September 11, 1893, 
viz. , the cutting of polished faces on pieces of 
diamond with some of the carbon powder from 
the cavities of the Caiion Diablo meteorite 
(Amer. Jour. Sci., Vol. XLVL, December, 1893; 
and Min. Resources U. S., 1893, pp. 683-685). 

In the meantime Professor Henri Moissan, 
of Paris, had been making his now celebrated 
experiments on the artificial production of 
diamonds from the cooling, under extreme 
pressure, of highly carbonated iron fused in a 
specially constructed electric furnace (Mineral 
Resources U. S., 1895, pp. 903-904). 

All these facts taken together form a remark- 
able series of confirmatory evidence of the 
views advocated by our late countryman in re- 
gard to the production of this most precious of 
gems, the origin of which has been so obscure a 
problem in mineralogy and geology. Another 
point of great scientific interest developed in the 
course of these investigations is the close simi- 
larity, both in composition and in structure, 
existing between some of these rarer igneous 
rocks of our globe and the extra-terrestrial vis- 
itants that come to us from space. 

Mr. G. F. Becker, in a recent letter, takes a 
different view of this subject and holds, that I 
have misinterpreted Professor Lewis, and that 
he did not regard the diamonds as due to car- 
bonaceous matter taken up from the shales. 

He claims that ' ' Lewis over and over again 
says that the diamond is as much n part of* the 
Kimberlite as its other component minerals." 
It is true that he did use such, an expression of 



. r a 



ser 
c the Kim' 
summing U] 
are in their 
notion of 
'kopjes' fron* <xkjo 
their having been carried up' 
rock from some deeper source below. The 
statement relates merely to ' the matrix of the 
diamond' — the subject of the article — not to 
the source of the carbon. Moreover, diamonds 
are not present in the Kimberlite of Syracuse, 
N. Y., or of Elliott County, Kentucky,* which 

* Is there a diamond field in Kentucky ? J. S. Dil- 
ler-G. F. Kunz, Science, Vol. X., 1887, pp. 140- 
142. 

Professor Lewis recognized as the same rock. 
He says (p. 56) : "In mineral composition, in 
eruptive character, in structure, in enclosures, 
the three rocks are identical. " It is plain, there- 
fore, that he did not regard diamonds as an essen- 
tial ingredient of Kimberlite. As to their source 
being carbon derived from the shales, it is true 
that Professor Lewis does not in these papers 
distinctly so assert, though he refers frequently 
and pointedly to the association of diamonds 
with the penetrated and included shales. But 
in personal conversation, [at a period between the 
dates of his two papers, and before he had even 
heard of the very suggestive experiment of Sir 
Henry Koscoe, Professor Lewis expressed to 
the writer his definite belief that such was their 
origin. The knowledge of this fact may have 
led me to state this view as held by Professor 
Lewis more clearly than appears on the face 
of his paper, and doubtless explains the perplex- 
ity that Mr. Becker expresses as to how he and 
I can read the article differently. 

Mr. Becker says: "I consider the diamonds 
as much a part of the Kimberlite as zircons are 
a part of granites." This may be Mr. Becker's 
view ; and he is a high authority, with whom I 
would not lightly disagree ; but it can hardly 
be claimed as the view of Professor Lewis, 
wher he asserts (as above noted) the absolute 
identity of the diamond-bearing Kimberlite of 
Africa with the non-diamond-bearing rocks of 
Syracuse and Kentucky. The question is not 
whether the diamonds (in Africa) are * a part 
of the Kimberlite.' Undoubtedly they are so, 
there ; but how came they to be so at that lo- 
cality and not at the others? This subject was 
fully discussed by the writer in ' Gems and 
Precious Stones of North America,' pp. 32-34, 
in connection with the examinations made by 
Mr. Diller and mylelf in 1887, as to the possi- 
ble occurrence of diamonds in Kentucky, as 
suggested by the similarity of the rock. It was 
there shown that, while the shales penetrated 
by the African Kimberlite had 37.50 per cent, 
of carbon, those traversed by the Kentucky 
Kimberlite contained but 0.68 per cent. The 
same rock breaks through a body of shale in 
two localities, the one rich in carbon, the other 
poor ; the intruding rock is fitted with dia- 
monds in the former case and none appear in 
the latter. 

Professor Lewis observes (p. 8) : li The rock 
(at Kimberley) appears in two types, one not 
bearing diamonds, the other diamantiferous, 



of carbon, those traversed by the Kentucky 
Kimberlite contained but 0.68 per cent. The 
same rock breaks through a body of shale in 



- » n » — i 



_ _ i 'j • . 



J 1 



■* ■« ■!■ H I 



poor ; the intruding rock is fitted with dia- 
monds in the former case and none appear in 
the latter. 

Professor Lewis observes (p. 8) : " The rock 
(at Kimberley) appears in two types, one not 
bearing diamonds, the other diamantiferous, 
and the distinction between them is suggestive. 
Both occur in the same mine and are dark, 
compact, heavy rocks, closely resembling one 
another and differing mainly in the fact that 
one is free from enclosures of foreign substance, 
while the other is full of fragments of shale and 
other impurities. It is the latter which is dia- 
mantiferous." On p. 46 he notes the fact that 
the fragments of shale included in the igneous 
rock have lost their carbonaceous matter; and 
on p. 51 he cites as of great interest the observa- 
tion and experiment of Professor Roscoe, else- 
where noted, as to the extraction of a hydro- 
carbon from the 'blue ground.' These refer- 
ences alone would indicate Professor Lewis' 
views, even apart from his own statement of 
them to the writer. 

Mr. Becker also alludes to the broken crystals, 
as repeatedly seen by him in separate frag- 
ments enclosed or embedded in the rock, and as 
not being considered rarities at Kimberley. 
These occurrences, however, may well be due 
to the very causes treated of by Professor 
Lewis in explaining the brecciated character of 
the rock (p. 54 and above noted), especially the 
first and third, the latter in particular, ' subse- 
quent explosions and movements in the crater ' 
below. Any such action sufficient to break up 
the Kimberlite into the likeness of a breccia 
would easily shatter the highly cleavable dia- 
mond crystals and bring about the condition 
seen and described by Mr. Becker. 

It may not be out of place here to recall an 
instance where, in another locality, the occur- 
rence of diamond may be connected with a 
similar outbreak of igneous rock through beds 
containing carbon. In a paper, < On Bohemian 
Garnets,' read by me before the American 
Institute of Mining Engineers, and published in 
their Transactions for February, 1892, mention 
was made of a diamond crystal found in 1870 
among a number of the pyrope garnets which 
are derived from the decomposition of peridotite 
rock. After being disputed and identified, it 
was deposited in the public museum at Prague. 
The decomposed serpentinous rock has evi- 
dently been transported from the north (prob- 
ably by glacial action) and there are found, at 
a distance of twenty or thirty miles in that di- 
rection, basaltic outflows that have broken 
through the coal measures. Here, again , is a 
suggestion of similar conditions, and the occur- 
rence of this single crystal is not without 
interest in such a connection. 

It is a matter for national pride that this re- 
markable investigation should have been made 
by an American scientist ; and a debt of grati- 
tude is due both to the great English meteor- 
ologist—the editor, Professor Bonney for his 

labor of love, alike to science and to a deceased 
friend, and also to Mrs. Lewis, who has so care- 
fully sought to prepare and make public these 
papers of her brilliant and lamented husband. 

George F. Kunz. 

Nkw Yokk. 



Sci 3G F 

THE GENESIS OF THE DIAMOND. 

There has recently been published a volume 
of small size, but of especial interest and im- 
portance, in regard to the origin of diamonds. 

This is none other than the posthumous issue 
of the full papers of the late Professor H. Car- 
vill Lewis, edited by his friend, Professor T. G. 
Bonney, of London. (Title as foot-note.*) It 
* Papers and notes on the ' Genesis and Matrix of 
the Diamond. ' By the late Henry Carvill Lewis, 
M.A., F.G.S., Professor of Mineralogy in the Acad- 
emy of Natural Scsences, Philadelphia, Professor of 
Geology in Haverford College, U. S. A. Pages xvi+ 
72. 2 Plates. London, 1897. Edited from his un- 
published MSS.,by Professor T. G. Bonney, D.Sc. 
LL.D., F.R.S., &c. Longmans, Green & Co., London 
and Bombay. 1897. 

Will be remembered that Professor Lewis was 
the first to present a clear and definite theory of 
the origin of the South African diamonds, as re- 
sulting from the intrusion of igneous rocks into 
and through carbonaceous shales, and the crys- 
tallization of the carbon throughout the rock as 
it cooled, from hydrocarbons distilled from the 
shale that had been broken through. These 
views, now for the most part accepted, and sub- 
sequently confirmed by other and very interest- 
ing parallel* discoveries, -'he presented in two 
papers read before the British Association for 
the Advancement of Science at its meetings held* 
in 1886, at Birmingham, and in 1887, at Man- 
chester. Before he was able, however, to pre- 
pare them for publication and carry them to the 
greater completeness that he desired, Professor, 
Lewis succumbed to an attack of typhoid fever, 
which removed one of the most brilliant and 
capable of the rising scientists of this country. 
Agreeably to his expressed wishes, his material 
was entrusted to his friend and co-laborer, Pro- 
fessor George H. Williams, of Johns Hopkins 
University ; but, by a strange fatality, before 
the latter had time to arrange and edit these 
papers he, too, fell a victim to the same disease, 
in 1894. The work was then committed to 
Professor Bonney and is at last given to the sci- 
entific world. 

The book consists of an introductory note by 
Mrs. Lewis ; a preface by Professor Bonney*; tt*e 
two papers of Professor Lewis himself, with 
some later notices and references by the editor ; 
a brief account of a similar material from other 
localities, belonging to Professor Lewis— also by 
the editor ; a closing note on some other MSS. 
of Professor Lewis, and a fu)l index* -There 
are also two ptates and a. Dumber of smaller il- 
lustrations, the latter from Professor Lewis' own 

drawings. 

The first paper, ■ On a diamond-bearing peri- 
dotite and on the history of the diamond * (1886), 
is brief, dealing with the general character and; 
occurrence of the diamantiferous rock at I£im-\ 
berley, and outlining Professor Lewis' theory. 

The second paper, l The matrix of the 
diamond ' (1887), is more extended and goes 
into an exhaustive discussion and comparison of 
the various aspects, contents and alterations of 
the rock, which he finds to be different from 
any previously described, and, therefore, pro- 



M 



■M 



of Professor Lewis, and a lull index. 'xnere 
are also two plates and a, "nunijb'er of smaller il- 
lustrations, the latter from Professor Lewis' own 
drawings. 

The first paper, c On a diamond-bearing peri- 
do tite and on the history of the diamond * (1 886), 
IsHBrieT ,~cTealmg wifOnTgeneral characWImaT" 
occurrence of the diamantiferous rock at Kim**, 
berley, and outlining Professor Lewis' theory. 
The second paper, ' The matrix of the 
diamond ' (1887), is more extended and goes 
into an exhaustive discussion and comparison of 
the various aspects, contents and alterations of 
the rock, which he finds to be different from 
any previously described, and, therefore, pro- 
poses for it the name of Kimberlite. Its main 
character is that of a highly basic porphyritic 
peridotite, filled* with •. olivine v cry^tajfr an4 
grains, more or less altered and various other 
minerals — serpentine, tremolite, etc., with 
bronzite, rutile, perofskite, pyrope garnets, 
micaceous minerals and other forms, and at 
times brecciated in structure, filled with frag- 
ments of carbonaceous „ shale brougM up from 
below. The shales "are of Triassic age, the 
1 Karo beds ' of that region, and the intrusion 
of the peridotite in the great < pipes ' or chim-* 
neys that constitute the mines is therefore 
proved to be of a later, though not exactly de- 
termined period. 

The question has sometimes been raised 
whether the diamonds themselves may not have 
been carried up from a deeper source in rock 
below, instead of originating in the peridotite ; 
and the occurrence of broken crystals has Been 
cited in support of this view. Professor Lewis, 
however, disposes very completely of this idea 
in two ways : He refers to the well-known fact 
that each of the great mines or ' pipes ' yields 
diamonds that have, in some respects^ a type of 
character peculiar to that one arid different from 
the others, so that African experts and even 
those who have never been there can recognize 
from which mine any diamond has come. 
Further, as to the broken crystals, he shows 
r that breakage not unfrequently occurs after the 
diamonds are removed from the rock, and 
points out that this is a result of strain in their 
formation, as indicated by microscopical and 
optical examination, and that such a condition 
is known to produce ruptures and explosions in 
other minerals. It may be added hare, al- 
though Professor Lewis does not speak of it, 
that many crystals must be broken in the blast- 
ing of the rock, the shoveling and the carting 
of the loosened material, and the various me- 
chanical processes employed at the mines, and 
that pieces of such broken crystals would be 
separated and scattered to various parts of the 
immense dumping and weathering floors, never 
to be recognized as fragments of the same one 
when finally recovered, perhaps at very differ- 
ent times. 

The rock itself is a dark green, compact ma- 
terial, resembling serpentine and containing a 
large proportion of olivine, in grains and crys- 
tals ; several green minerals that are not con- 
spicuous, from the resemblance of their color, 
from the ground-mass (enstatite, chrome-diop- 
side, smaragdite and blastite); a mica, probably 
biotite, more conspicuous and quite abundant, 
and frequent grains of prope garnet, sometimes 
of gem quality and great beauty, and miscalled 
( Cape Rubies.' Of smaller disseminated min- 



ments of carbonaceous shale brought) up from 
below. The shales "are of Triassic age, the 
1 Karo beds » of that region, and the intrusion 
of the peridotite in the great ' pipes ' or chim-" 
neys that constitute the mines is therefore 
proved to be of a 1».t,p.r fT i/\nnpT» ™~+ r _„ ? i.i— *. 
termined period. 

The question has sometimes been raised 
whether the diamonds themselves may not have 
been carried up from a deeper source in rock 
below, instead of originating in the peridotite ; 
and the occurrence of broken 'crystal's has Been 
cited in support of this view. Professor Lewis, 
however, disposes very completely of this idea 
in two ways : He refers to the well-known fact 
that each of the great mines or l pipes ' yields 
diamonds that have, in some respects^ a type of 
character peculiar to that one and different from 
the others, so that African experts and even 
those who have never been there can recognize 
from which mine any diamond has come. 
Further, as to the broken crystals, he shows 
that breakage not unfrequently occurs after the 
diamonds are removed from the rock, and 
points out that this is a result of Strain in their 
formation, as indicated by microscopical and 
optical examination, and that such a condition 
is known to produce ruptures and explosions in 
other minerals. It may be added here, al- 
though Professor Lewis does not speak of it, 
that many crystals must be broken in the blast- 
ing of the rock, the shoveling and the carting 
of the loosened material, and the various me- 
chanical processes employed at the mines, and 
that pieces of such broken crystals would be 
separated and scattered to various parts of the 
immense dumping and weathering floors, never 
to be recognized as fragments of the same one 
when finally recovered, perhaps at very differ- 
ent times. 

The rock itself is a dark green, compact ma- 
terial, resembling serpentine and containing a 
large proportion of olivine, in grains and crys- 
tals ; several green minerals that are not con- 
spicuous, from the resemblance of their color, 
from the ground-mass (enstatite, chrome-diop- 
side, smaragdite and blastite); a mica, probably 
biotite, more conspicuous and quite abundant, 
and frequent grains of prope garnet, sometimes 
of gem quality and great beauty, and miscalled 
' Cape Rubies. ' Of smaller disseminated min- 
erals are to be noted perovskite, quite frequent, 
and magnetite, chromite, ilmenite and picotite, 
less so, though common. Rare and minute oc- 
currences are patite, epidote, orthite, tremolite, 
tourmaline, rutile, sphene, leucoxene. As de- 
composition products there are serpentine and 
calcite, abundant, and zolites, chalcedony and 
talc ; also cyanite (?) These, with the dia- 
monds and the included fragments of carbona- 
ceous shale, make up the contents of this re- 
markable rook;. 

Professor Lewis then goes into a detailed 
account of the mode of occurrence of these 
minerals, beginning with the most conspicuous 
species—the olivine— which is remarkable for 






>■ . 



^_# 



rtci 37 F 

its fine cleavage-surfaces and very interesting 
in its alterations. ' These are chiefly (1) into 
serpentine, proceeding from without inward, 
and penetrating along crevices and fractures, 
also sometimes in the form of chrysotile pro- 
ducing a velvety border Or coating to the grain ; 
(2) tremolite, more internal, the fibrous struc- 
ture developing parallel to the vertical axis 
and domes of the olivine crystals ; (3) when 
both these alterations are present and have 
gone so far as to obliterate most or all of the 
olivine, a talc-like substance intervenes be- 
tween them in which are developed minute 
needles of rutile, arranged parallel to the faces 
of the olivine crystal. The rock contains every 
stage of these changes from pure bright unal- 
tered olivine to those forms that have borders 
of serpentine or chrysotile, or incipient tremo- 
lite fibers within, to the complete alteration 
just described. The relation of all these to 
similar phenomena in other rocks, and in 
meteorites, is discussed with much fulness. 

Professor Lewis then takes up the Smarag- 
dite, chrome-diopdite, bastite and enstatite (or 
bronzite, for it is just on the line between the 
two varieties). The two first named are, in 
some cases, fine enough in color and clearness 
to yield gems, and also sometimes the bron- 
zite ; all are colored by chromium. The diop- 
side occasionally gives rise to calcite by alter- 
ation, 

The mica is next considered ; as all who are 
familiar with the rock are aware, it is the most 
prominent of the contained minerals to the eye. 
It is somewhat anomalous in character, being 
chemically a biotite, but optically nearer to 
phlogopite. It occurs in several distinct ways: 

(1) as included crystalline masses or plates, 
apparently an original ingredient of the rock ; 

(2) surrounding grains of pyrope ; (3) rarely, 
as a result of the alteration of enstatite ; and 
(4) as a metamorphic product from the included 
fragments of shale, and the first form has pro- 
duced, by hydration, the vermiculite variety 
called vaalite, which occurs freely in the de- 
composed peridote so largely known as the 
' blue-ground.' 

After referring to the pyrope garnets, and 
suggesting that the various garnetiferous ser- 
pentines are doubtless derived from the decom- 
position of similar peridotites, as further indi- 
cated by their likewise containing olivine, bron- 
zite, chrome-diopside, etc. , he mentions another 
variety of garnets as found in this rock, very 
small, very brilliant, very hard, colorless or 
greenish, and extremely difficult to distinguish 
from small diamonds. These Professor Lewis 
is inclined ro refer to dimantoid. (?) 

An interesting part of this discussion next 
follows, in relation to the perovskite, which is 
pretty abundant in small crystals, of cubical 
habit. Professor Lewis gives much attention 
and a number of drawings to the optical fea- 
tures of this species, and strongly inclines to 



i - 



111LL1 1 UUUUllJ LU 11JU W/l'Mui garnets, aud 

suggesting tliat t,lio vnrious garnetiferous ser- 
pentines are doubtless derived from the decom- 












.~:,i^+; + . 



T1TH+ T-l 



■* w i ii N^«gwa» 



cated by their likewise containing olivine, bron- 
zite, chrome-diopside, etc., he mentions another 
variety of garnets as found in this rock, very 
small, very brilliant, very hard, colorless or 
greenish, and extremely difficult to distinguish 
from small diamonds. These Professor Lewis 
is inclined ro refer to dimantoid. (?) 

An interesting part of this discussion next 
follows, in relation to the perovskite, which is 
pretty abundant in small crystals, of cubical 
habit. Professor Lewis gives much attention 
and a number of drawings to the optical fea- 
tures of this species, and strongly inclines to 
the view that regards perovskite as a highly 
twinned orthorhombic mineral and not isomet- 
ric save in external aspect. This has long been 
a mooted point, and these observations are an 
important contribution. Of much interest also 
are the chemical and genetic relations of this 
species as here presented ; the crystals often 
enclose grains of what Professor Lewis terms a 
titanic spinellid, perhaps a titaniferous magne- 
tite, perhaps ilmenite, indicating a derviation 
therefrom ; they also, in some cases, lie in a 
curious manner, upon or around partially al- 
tered olivine crystals. The remark is made 
that, while perovskite is familiar in various 
non-feldspathic igneous rocks, it has not been 
found in peridotite until Professor Williams 
recognized it in the peculiar rock from Syra- 
cuse, N. Y., and that later Professor Lewis 
identified it in the similar rock from Isom's 
Creek, Kentucky, where it had been previously 
regarded as anatase. These three rocks, those 
just named and the African, are- the only known 
occurrences of what is here named Kimberlite. 
The articles goes on to show that in basic 
eruptive rocks the titanium takes the form 
of perovskite, while in acid rocks it forms 
sphene • in intermediate ones it developa 
ilmenite or titanic iron ; and these deductions 
harmonize precisely with important experi- 
ments of Gourgeois, in the artificial produc- 
tion of titanium minerals. 

After going into some particulars as to the 
minor minerals found in this rock, Professor 
Lewis then takes up the base or ground mass 
and discusses it minutely. He terms it 'a 
more or less homogeneous serpentinous mass,' 
very difficult to study by reason of its decom- 
posed condition, consisting now of a mixture of 
serpentine with calcite and some other pro- 
ducts of alteration, the original structure being 
wholly lost. , . 

Pragmental enclosures are frequent, 'both 
of the adjoining shale and diabase, and also of 
more deeply seated granite, gneiss, eclogite, 
and other related rocks.' Of these the shale 
predominates, sometimes making the rock a 
breccia. The shale itself is highly charged with 
carbon, so as to be quite combustible ; but the 
included fragments are altered, having lost their 
carbon and become harder, sometimes even 
metamorphosed to a micaceous structure, as 
before referred to. In size they vary from 
large masses, in the upper part of the mines, 
called by the workers « floating-reef, ' to small 
fragments, diminishing in number and size in 
descending. 

Professor Lewis goes into very detailed petro- 
graphical and chemical discussion as to the 
original character of the rock, in which it is 



■■a^~ 



•■ered olivine crystals. The remark is made 
hat, while perovskite is familiar in various 



— *- -xtv n ' i-i^i ' vx gr 



p auiii^ is iiw ona rocKS, it has no t "B een " 
found in peridotite until Professor Williams 
recognized it in the peculiar rock from Syra- 
cuse, N. Y., and that later Professor Lewis 
identified it in the similar rock from Isom's 
Creek, Kentucky, where it had been previously 
regarded as anatase. These three rocks, those 
just named and the African, are- the only known 
occurrences of what is here named Kimberlite 
The articles goes on to show that in basic 
eruptive rocks the titanium takes the form 
of perovskite, while in acid rocks it forms 
sphene; in, intermediate ones it develops 
dmenite or titanic iron ; and these deductions 
harmonize precisely with important experi- 
ments of Gourgeois, in the artificial produc- 
tion of titanium minerals. 

After going into some particulars as to the 
minor minerals found in this rock, Professor 
Lewis then takes up the base or ground mass 
and discusses it minutely. He terms it 'a 
more or less homogeneous serpentinous mass ' 
very difficult to study by reason of its decom- 
posed condition, consisting now of a mixture of 
serpentine with calcite and some other pro- 
ducts of alteration, the original structure being; 
wholly lost. s 

Fragmental enclosures are frequent, 'both 
of the adjoining shale and diabase, and also of 
more deeply seated granite, gneiss, eclogite 
and other related rocks. ' Of these the shale 
predominates, sometimes making the rock a 
breccia. The shale itself is highly charged with 
carbon, so as to be quite combustible ; but the 
included fragments are altered, having lost their 
carbon and become harder, sometimes even 
metamorphosed to a micaceous structure, as 
before referred to. In size they vary from 
large masses, in, the upper part of the mines ' 
called by the workers 'floating-reef,' to small 
fragments, diminishing in number and size in 
descending. 

Professor Lewis goes into very detailed petro- 
graphical and chemical discussion as to the 
original character of the rock, in which it is 
hardly possible to follow him in a review, and 
Ending no known rock that presents identical 
characters, he proposes for it the name of 
K.mberlite. This he designates as 'a porpby- 
ritio volcanic peridotite of basaltic structure ' 
and notes three forms of its occurrence : (1) 
Kimberlite proper, a typical porphyritic lava ; 
(2) Idmberlite breccia, the same rock broken 
and crushed by volcanic movements and 
crowded with included fragments of shale • (3) 
Kimberlite tuff, the fragmental and tufaceous 
portion of the same rock. These varieties 
graduate into each other, and all occur together 
in the same neck or crater, the second, how- 
ever, being most abundant and most productive 

of diamonds. 



._ — >™-»_ 



~ ■ — - 



sci 38 F 

He treats of the origin of the brecciated 
structure which has caused much discussion, 
some geologists regarding the whole rock as a 
sort of tufa or volcanic mud, while others hold 
that it is a true outpouring lava that has car- 
ried up fragments of the rocks broken through 
it its course, and has since been largely decom- 
posed. Professor Lewis urges the latter theory 
strongly, and supports it by many arguments ; 
while the editor, Professor Bonney, evidently 
inclines to the other view, advocated by Pro- 
fessor W. H. Hurdlestone, in 1885, and by 
some others. There is not space here to review 
Professor Lewis' several arguments for the true 
igneous character of the Kimberlite and against 
the tufaceous theory. The one to which Pro- 
fessor Bonney accords the chief importance is 
the identity of the rock with that from Syra- 
cuse, New York, and Elliott county, Kentucky, 
where it occurs in actual dikes, such as are 
found in tufas. The brecciated character, 
which is so marked, is referred by Professor 
Lewis to three causes, acting either separately 
or perhaps together. These are (1) rapid cool- 
ing and shrinkage; (2) ' friction brecciation,' 
from contact with the wall-rock ; and (3) sub- 
sequent movement and explosions in the crater 
itself, below. He illustrates and parallels the 
first of these from meteorites, to some of which 
this rock bears marked resemblance both in 
structure and contents, and the others from 
-well-known occurrences in terrestrial volcanic 
rocks. 

The third section of the volume is occupied 
with a detailed account, from specimens and 
notes of Professor Lewis, of the two other 
known occurrences of Kimberlite, at Syracuse, 
N. Y., and Willard, Ky. The identity of these 
with the African rock, in almost all particulars, 
is remarkable, and as they form definite eruptive 
tufas Professor Lewis' view as to :he latter is 
strongly confirmed. 

It remains only to call attention to other and 
later facts which tend to bear out the views pre- 
sented in this remarkable posthumous article. 

The presence of a residual hydrocarbon in thie 
rock of the African diamond mines was shown 
by an interesting and important observation of 
Sir Henry E. Roscoe (Proc. Lit. and Phil. Soc. 
of Manchester, XXIV., 1885, p. 6), which is al- 
luded to by Professor Lewis in his second paper, 
and has frequently been cited in discussions of. 
the subject. He found that the ' blue-ground ' 
on treatment with hot water yielded an aro- 
matic hydrocarbon, which he was able to sepa- 
rate by digesting the l blue-ground ' with ether 
and evaporating the solution. It then appeared 
as a crystalline aromatic solid, burning with a 
smoky flame (showing it rich in carbon) volatile, 
and melting at 50° C. 

The bearing of this fact upon Professor Lewis' 
theory is clear. (?) He holds that the igneous 
rock, breaking through the highly carbonaceous 
Karoo shales (37.50 p. C. of carbon ; Whitfield, 
U. S. Geological Survey ; G. and Pres. Stat. 
North America, 1889, p. 33) became charged 
with volatilized hydrocarbons distilled from the 
shale, and that in cooliug these had crystallized 
partly into diamonds and partly into the many 

carbonadons, larger and smaller, which are dis- 
tributed through the rock. Professor Roscoe' s 



^J^^^^^^^^^^^^«^»M^« 



Jl> 



as a crystalline aromatic solid, burning with a 
smoky flame (showing it rich in carbon) volatile, 
and melting at 50° C. 

The bearing of this fact upon Professor Lewis' 
theory is clear. (?) He holds that the igneous 
rock, breaking through the highly carbonaceous 
Karoo shales (37.50 p. C. of carbon ; Whitfield, 
U. S. Geological Survey ; G. and Pres. Stat. 
North America, 1889, p. 33) became charged 
with volatilized hydrocarbons distilled from the 
shale, and that in cooling these had crystallized 
partly into diamonds and partly into the many 
carbonadons, larger and smaller, which are dis- 
tributed through the rock. Professor Roscoe's 
material strongly confirms this theory, which, 
indeed, he himself propounded. 

In 1886 a meteorite fell at Novo Yrei (Sep- 
tember 22d) in the province of Pensa, Russia, 
which was found to contain about 1 per cent, of 
diamond carbon, in the form of gray particles.* 

* DaubreJJ's discussion of the analogy of the occur- 
rence of the diamond in the meteorites and in the 
South African Kimberlite was the next important 
paper on this subject. (Comptes Rendus 110-18, 
1890. ) 

In 1887 Mr. Fletcher (Miner alogical Magazine, 
7, 121) described the new mineral l Cliftonite ' 
— a black substance with a hardness of 2.5 and 
a density of 2.12 occurring in cubes with faces 
of the dodecahedron or tetrahexahedron in the 
meteorite of Youndegin, West Australia. This 
suggested a graphite alteration of a diamond — a 
view taken by Brezina (Am. Mus. Wien., IV., 
102, 1889) regarding this new species and cer- 
tain graphite crystals of cubic type, observed 
long before in the Arva meteorite and regarded 
as pseudomorpho after pyrite, by Haidinger 
(Pogg. , 67, 487, 1846), but later by Rose, as after 
diamond (Beschr. Meteor., 40, 1864). Similar 
crystals were also known in the Sevier iron of 
Cooke county, Tenn. n 

In 1891 the discovery of diamond, or at least 
of diamond carbon, in some quantity in the 
meteoric iron of Canon Diablo, Arizona, was 
announced by the late Professor A. E. Foote 
(Amer. Jour. Science, Vol. XIII., July, 1891, pp. 
413-417) and Dr. George A. Koenig. In July, 
1892 (Science, p. 12), Dr. O. W. Huntington 
gave further experiments on the same material, 
confirming the decisions of Professors JFoote and 
Koenig ; and in December of the same year 
similar results were published by M. C. Friedel 
(Bulletin de la Soc. Francaise de Miner alogie, N. 
9, p. 258). A crucial test was then proposed 
by G. F. Kunz, of New York, and carried out 
in the presence of Dr. Huntington, at the 
World's Fair at Chicago, September 11, 1893, 
viz. , the cutting of polished faces on pieces of 
diamond with some of the carbon powder from 
the cavities of the Canon Diablo meteorite 
(Amer. Jour. Sci., Vol. XLVL, December, 1893; 
and this report for 1893, pp. 683-685). 

In the meantime Professor Henry Moissan, 
of Paris, had been making his now celebrated 
experiments on the artificial production of 
diamonds from the cooling, under extreme 
pressure, of highly carbonated iron fused in a 
specially constructed electric furnace (this re- 
port, 1895, pp. 903-904). 

All these facts taken together form a remark- 
able series of confirmatory evidence of the 
views advocated by our late countryman in re- 
gard to the production of this most precious of 
gems, the origin of which has been so obscure a 
nif lenLlii_niinerL ogv and geology. Anothei 



■/ ■ 



paper ou this subject. (Comptes Rendus 110-18, 
1890. ) 

In 1887 Mr. Fletcher {Miner alogical Magazine, 
7, 121) described the new mineral l Cliftonite 7 
— a black substance with a hardness of 2.5 and 
aTTEftsity 6r27T l 2 occiirrmg m cUbes"WTTTT fftesr ~ 
of the dodecahedron or tetrahexahedron in the 
meteorite of Youndegin, West Australia. This 
suggested a graphite alteration of a diamond — a 
view taken by Brezina (Am. Mus. Wien., IV., 
102, 1889) regarding this new species and cer- 
tain graphite crystals of cubic type, observed 
long before in the Arva meteorite and, regarded 
as pseudomorpho after pyrite, by Ilaidinger 
(Pogg. ? 67, 487, 1846), but later by Kose, as after 
diamond (Beschr. Meteor., 40, 1864). Similar 
crystals were also known in the Sevier iron of 
Cooke county, Tenn. n 

In 1891 the discovery of diamond, or at least 
of diamond carbon, in some quantity in the 
meteoric iron of Canon Diablo, Arizona, was 
announced by the late Professor A. E. Foote 
(Amer. Jour. Science, Yol. XIII., July, 1891, pp. 
413-417) and Dr. George A. Koenig. In July, 
1892 (Science, p. 12), Dr. O. W. Huntington 
gave further experiments on the same material, 
confirming the decisions of Professors JFoote and 
Koenig ; and in December of the same year 
similar results were published by M. C. Friedel 
(Bulletin de la Soc. Francaise de Mineralogie } N. 
9, p. 258). A crucial test was then proposed 
by G. F. Kunz, of New York, and carried out 
in the presence of Dr. Huntington, at the 
World's Fair at Chicago, September 11, 1893, 
viz. , the cutting of polished faces on pieces of 
diamond with some of the carbon powder from 
the cavities of the Canon Diablo meteorite 
(Amer. Jour. Set. , Vol. XLVL , December, 1893; 
and this report for 1893, pp. 683-685). 

In the meantime Professor Henry Moissan, 
of Paris, had been making his now celebrated 
experiments on the artificial production of 
diamonds , from the cooling, under extreme 
pressure, of highly carbonated iron fused in a 
specially constructed electric furnace (this re- 
port, 1895, pp. 903-904). , . . - 

All these facts taken together form a remark- 
able series of confirmatory evidence of the 
views advocated by our late countryman in re- 
gard to the production of this most precious of 
gems, the origin of which has brenso obscure a 
problem in mineralogy and geology. Another 
point of great scientific interest developed in the 
course of these investigations is the close simi- 
larity, both in composition and in structure, 
existing between some of these rarer igneous 
rocks of our globe and the extra-terrestrial vis- 
itants that come to us from apace. 



^ci 39 * F 
It is a matter for national pride that this re- 
markable investigation should have been made 
by an American scientist, and a debt of grati- 
tude is due both to the great English meteor- 
ologist-, the editor, Professor Bonney, for his 
labor of love, alike to science and to a deceased 
friend, and also to Mrs. Lewis, who has so care- 
fully sought to prepare and make public these 
papers of her brilliant and lamented husband. 

George F. Kunz. 



SCIENCE 

EDITORIAL DEPARTMENT 



Garr son-on-Hudson, N.Y. June 5. 1897 



Dear Mr. Kunz:- 



Would you consent bo write a notice of the posthumous pape** 
by H. C Lewis on the Diamond, edited "by Prof. Ponne'* which 
we have just received from the publishers?. 

Very truly yours, 



Mr. George F. Xunz 
New York Ciy 




(jiult CcdkH 



THIRTEENTH YEAR Of SUCCESS 




No. 



- 

TJEtE 



FROM 




JVewYopkGlty 

WV £747 f U 

*UlGEIlC* 




From 






■ ■ 



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/-m 



LITERATURE. 



Papers and Notes on lhe-G,cncsis of the Dia- 
mond. By the late Heofry Carvill Lewis. 
Edited by Prof. T. G. Bonney. Longmans, 
Green & Co. 1897. 

Abstracts of these interesting papers ap- 
peared about ten years ago, but a singularly 
unhappy fate has attended the production of 
the complete texts. The talented young 
geologist who wrote them, and whose work 
on the 'Glacial Geology of Great Britain' was 
reviewed in these columns in 18i5, died in 
18SS, committing his manuscript to George 
H. Williams, whom also his colleagues have 
to lament. The manuscripts were then com- 
mitted to Prof. Bonney. 

In his preface the editor announces as Mr. 
Lewis's view of the genesis of the diamond 
that it is due to "the action of an extremely 
basic rock upon carbonaceous material." As 
the editor must have read the papers, and 
these are clear in their statements, one can 
only say that Mr. Bonney's representation 
is singularly misleading. Lewis never saw 
the Kimberley mines, but examined suites 
of specimens with most painstaking care, 
and his conclusions are in the main geologi- 
cally correct. The mines are volcanic 
"necks," or the conduits of ancient volca- 
noes, filled for the most part with an igneous 
breccia which arose from the breaking up of 
solid lava crusts in liquid lava. With the 
breccia are mingled fragments of wall rock. 
Much of the wall rock is a bituminous shale, 
and some geologists have ascribed the for- 
mation of the diamonds to the action of the 
igneous rock on this material. Not so 
Lewis, who wrote: "The diamonds are as 
much a part of the Kimberley rock as bio- 
tite, garnet, titanic and chromic iron, and 
perovskite, and, like these minerals, may be 
considered a rock ingredient." He also 
points to the abundance of minute, almost 
microscopic, crystals of black diamond as 
evidence that these were not enclosures 
brought up from some other matrix, such as 
gneiss or itacolumite. The shale, he truly 
says, is most plentiful near the top of the 
Kimberley mine, and less frequent in the 
deeper portions; while the diamonds "con- 
tinue iust as abundant, if not more so, the 



Abstracts of these interesting papers ap- 
peared about ten years ago, but a singularly 
unliappy fate has attended the production of 
the complete texts. The talented young 
geologist who wrote them, and whose work 
on the 'Glacial Geology of Great Britain* was 
reviewed in these columns in 1S95, died in 
18SS, committing his manuscript to George 
H. Williams, whom also his colleagues have 
to lament. The manuscripts were then com- 
mitted to Prof. Bonney. 

In his preface the editor announces as Mr. 
Lewis's view of the genesis of the diamond 
that it is due to "the action of an extremely 
basic rock upon carbonaceous material." As 
the editor must have read the papers, and 
these are clear in their statements, one can 
only say that Mr. Bonney's representation 
is singularly misleading. Lewis never saw 
the Kimbeiiey mines, but examined suites 
of specimens with most painstaking care, 
and his conclusions are in the main geologi- 
cally correct. The mines are volcanic 
"necks," or the conduits of ancient volca- 
noes, filled for the most part with an igneous 
breccia which arose from the breaking up of 
solid lava crusts in liquid lava. With the 
breccia are mingled fragments of wall rock. 
Much of the wall rock is a bituminous shale, 
and some geologists have ascribed the for- 
mation of the diamonds to the action of the 
igneous rock on this material. Not so 
Lewis, who wrote: "The diamonds are as 
much a part of the Kimberley rock as bio- 
titc, garnet, titanic and chromic iron, and 
perovskite, and, like these minerals, may be 
considered a rock ingredient." He also 
points to the abundance of minute, almost 
microscopic, crystals of black diamond as 
evidence that these were not enclosures 
brought up from some other matrix, such as 
gneiss or itacolumite. The shale, he truly 
says, is most plentiful near the top of the 
Kimberley mine, and less frequent in the 
deeper portions; while the diamonds "con- 
tinue just as abundant, if not more so, the 
deeper the mines are explored." They are, 
according to Lewis, never found in, or espe- 
cially associated with, the foreign inclu- 
sions; and this is correct. As to the origin 
of the carbon, Lewis does not commit him- 
self. 

Lewis went astray in his interpretation of 
the fractured diamonds of these deposits. 
Some of the gems go to pieces spontaneously 
ifter they have been extracted; these speci- 
mens have, as a rule, a peculiar brownish 
x>lor, and are readily distinguished by ex- 
perts. The cause of the disintegration is 
rery probably included gas. The fragments 
af diamonds found in the rock itself are 
rarely if ever of this character, nor do they 
present any other peculiarity. They are in 
all respects comparable with the broken 
porphyritic crystals of other minerals which 
Lewis observed in the rock, and all these 
fractures are referable to the moment of ex- 
plosive expulsion of the lava from its deep-,, 
seated source. Such fracturing is common 
in igneous rocks. 

These papers give full attention to the 
mineralogical composition of the rock which 
Lewis named Kimberlite. It is chiefly com- 
posed of olivine and contains no feldspar, 
[t closely resembles some stony meteorites. 
Similar rocks are found in the United States, 
but the diamond has been detected in its 
original matrix only in the South African 
deposits. 







Sketches of Travel 



N 



,L 




9 



^t> 



luR 



Papers and Notes on the Genesis of the Dia- 
mond. By the late Henry Carvill Lewis. 
Edited by Prof. T. G. Bonney. Longmans, 
Green & Co. 1897. 

Abstracts of these interesting papers ap- 
peared about ten years ago, but a singularly 
unhappy fate has attended the production of 
the complete texts. The talented young 
geologist who wrote them, and whose work 
on the 'Glacial Geology of Great Britain' was 
reviewed in these columns in 1895, died in 
1888, committing his manuscript to George 
H. Williams, whom also his colleagues have 
to lament. The manuscripts were then com- 
mitted to Prof. Bonney. 

In his preface the editor announces as Mr. 
Lewis's view of the genesis of the diamond 
that it is due to "the action of an extremely 
basic rock upon carbonaceous material." As 
the editor must have read the papers, and 
these are clear in their statements, one can 
only say that Mr. Bonney's representation 
is singularly misleading. Lewis never saw 
the Kimberiey mines, but examined suites 
of specimens with most painstaking care, 
and his conclusions are in the main geologi- 
cally correct. The mines are volcanic 
"necks," or the conduits of ancient volca- 
noes, filled for the most part with an igneous 
breccia which arose from the breaking up of 
solid lava crusts in liquid lava. With the 
breccia are mingled fragments of wall rock. 
Much of the wall rock is a bituminous shale, 
and some geologists have ascribed the for- 
mation of the diamonds to the action of the 
igneous rock on this material. Not so 
Lewis, who wrote: "The diamonds are as 
much a part of the Kimberiey rock as I io- 
tlte, garnet, titanic and chromic iron, and 
perovskite, and, like these minerals, may be 
considered a rock ingredient." He also 
points to the abundance of minute, almost 
microscopic, crystals of black diamond as 
evidence that these were not enclosures 
brought up from some other matrix, such as 
gneiss or itacolumite. The shale, he truly 
says, is most plentiful near the top of the 
Kimberiey mine, and less frequent in the 
deeper portions; while the diamonds "con- 
tinue just as abundant, if not more so, the 
deeper the mines are explored." They are, 
according to Lewis, never found in, or espe- 
cially associated with, the foreign inclu- 
sions; and this is correct. As to the origin 
of the carbon, Lewis does not commit him- 
self. 

Lewis went astray in his interpretation of 
the fractured diamonds of these deposits. 
Some of the gems go to pieces spontaneously 
ifter they have been extracted; these speci- 
mens have, as a rule, a peculiar brownish 
solor, and are readily distinguished by ex- 
perts. The cause of the disintegration is 
rery probably included gas. The fragments 
af diamonds found in the rock itself are 
rarely if ever of this character, nor do they 
present any other peculiarity. They are in 
all respects comparable with the broken 
porphyritic crystals of other minerals which 
Lewis observed in the rock, and all these 
fractures are referable to the moment of ex- 
plosive expulsion of the lava from its deep- 
seated source. Such fracturing is common 
in igneous rocks. 



it must bj 
in spite 
204, wher 
spire of 
though "ij 
of the eldc 

Year-BooJci 
the Thin 
ed and 
London 
3o8. 

An inter* 
separates tJ 
that of the] 
The delay 
and we an 
tion of thesl 
"not less r.j 
lier years." 
scholarly m| 
introduced, 
of the Plea' 
to be publi? 
which reachl 
This will be 
lars. 

Much the gr 
ed "Introductfl 
sideration of a 
Edward III. to 
and to the histoi 
has less interest 
scholars; but still 
ject of corporation: 
"It was really aboil 
III. . . . that the 
ration, the lay persom 
stood), was painfull/ el^ 
have visited the beautil 
be interested in this 
burgesses of Wells] hadl 
town walled, embattled,] 
tie before this time [li 
Bath and Wells. (Ralp!' 
had applied for a license 1 
palace with wall and ba^ 
rets; and he succeeded 
His battlements still reml 
around them, as a monumj 
rable struggle oM.he foui 

At p. xxli Mr. Pike 
passage on peasants, "aj 
not often occur in the Y< 
sant, he says, is etymol 
tant of the country (p\ 
freeholder could not 
when an issue was to 
try (patria, pais}* tl 
for a word (parfol 
etymological coil 
rived from pagus 
sue to be tried 
tried by the pa\ 
not free and law] 

At p. 290, thej 
of a case involvjj 
attaint jury ofl 
original jury wj 

It is interest} 
1342 of names 
miliar. The mi 
Seggewyke, in 
Henry de Wall 
'Pioins Doraunj 
Bethum, or, asl 
thun and Betl 



IUU IU1W1 WUU 1WIU lUall LliL pllk.y. ailU 
these are clear in their- statements, one can 
only say that Mr. Bonney's representation 
is singularly misleading. Lewis never saw 
the Kimberley mines, but examined suites 
of specimens with most painstaking care, 
and his conclusions are in the main geologi- 
cally correct. The mines are volcanic 
"necks," or the conduits of ancient volca- 
noes, filled for the most part with an igneous 
breccia which arose from the breaking up of 
solid lava crusts in liquid lava. With the 
breccia are mingled fragments of wall rock. 
Much of the wall rock is a bituminous shale, 
and some geologists have ascribed the for- 
mation of the diamonds to the action of the 
igneous rock on this material. Not so 
Lewis;, who wrote: "The diamonds are as 
much a part of the Kimberley rock as bio- 
titc, garnet, titanic and chromic iron, and 
perovskite, and, like these minerals, may be 
considered a rock ingredient." He also 
points to the abundance of minute, almost 
microscopic, crystals of black diamond as 
evidence that these were not enclosures 
brought up from some other matrix, such as 
gneiss or itacolumite. The shale, he truly 
says, is most plentiful near the top of the 
Kimberley mine, and less frequent in the 
deeper portions; while the diamonds "con- 
tinue just as abundant, if not more so, the 
deeper the mines are explored." They are, 
according to Lewis, never found in, or espe- 
cially associated with, the foreign inclu- 
sions; and this is correct. As to the origin 
of the carbon, Lewis does not commit him- 
self. 

Lewis went astray in his interpretation of 
the fractured diamonds of these deposits. 
Some of the gems go to pieces spontaneously 
sifter they have been extracted; these speci- 
mens have, as a rule, a peculiar brownish 
:olor, and are readily distinguished by ex- 
perts. The cause of the disintegration is 
rery probably included gas. The fragments 
of diamonds found in the rock itself are 
rarely if ever of this character, nor do they 
present any other peculiarity. They are in 
all respects comparable with the broken 
porphyritic crystals of other minerals which 
Lewis observed in the rock, and all these 
fractures are referable to the moment of ex- 
plosive expulsion of the lava from its deep- 
seated source. Such fracturing is common 
in igneous rocks. 

These papers give full attention to the 
mineralogical composition of the rock which 
Lewis named Kimberlite. It is chiefly com- 
posed of olivine and contains no feldspar. 
It closely resembles some stony meteorites. 
Similar rocks are found in the United States, 
but the diamond has been detected in its 
original matrix only in the South African 
deposits. 



Sketches of Travel in Normandy and Maine. 
By Edward A. Freeman. "With illustra- 
tions from drawings by the Author, and a 
preface by W. H. Hutton, B.D., Fellow 
and Tutor of St. John's College, Oxford. 
Macmillan. 1897. $2.50. 

The historian Freeman was always great- 
ly interested in geography, in topography, 
and in buildings, as, indeed, an historian 
ought to b' His possession of considerable 
jneans enaL. i -iim to travel much, and he 
ised his jou- -$ to excellent advantage 
constant and jlose study of the local] 
fcvhich his historical interest was. 
many volumes of hislDEi 
this strong interest 
mcient structure 
Lre detaefcu 
:ta 



of the Plea 
to be publil 
which reach! 
This will be 
lars. 

Much the grl 
ed "Introductii 
sideration of a 
Edward III. to 
and to the histoi 
has less interest 
scholars; but still 
ject of corporation! 
"It was really aboul 
III. . . . that the' 
ration, the lay per<on\ 
stood), was painfull/ elj 
have visited the beautifl 
be interested in this 
burgesses of Wells] hadl 
town walled, embattled,! 
tie before this time [11 
Bath and Wells, (RalpJ 
had applied for a license^ 
palace with wall and ba1 
rets; and he succeeded 
His battlements still reml 
around them, as a monumj 
rable struggle oM.he foui 

At p. xxii Mr. Pike 
passage on peasants, "aj 
not often occur m the Y< 
sant, he says, is etymo] 
tant of the country (p\ 
freeholder could not 
when an issue was to 
try (patria, pais}, tl 
for a word (pa#0| 
etymological coV , 
rived from pagus\\ 
sue to be tried bj 
tried by the pai^ 
not free and lawl 

At p. 290, tin 
of a case involve 
attaint jury oj 
original jury wj 

It is interest] 
1342 of names 
miliar. The mi 
Seggewyke, in. 
Henry de Wall 
Thorns Doraun] 
Bethum, or, asj 
thun and Bed 
Westmorland), 
among those wl 
our readers. 

In a strictly 
volume has less' 
predecessors. 

— Proposals 
cum,' signed, 
Mr. David 
lege, are n; 
begin by 
felt by 
Platonicus 
Aristotelicl 
of Attt's '] 
adverted 
any pricj 
portant^ 
rangej 
tain? 
re&