OCTOBER 29, 1897.] 
“‘Tf so, the atmosphere would be the original 
source of the diamond.’’ A little later he re- 
marks : 
“The earlier theories as to the origin of the 
diamond have, in the light of new facts, quite 
given way to the theory that the diamonds be- 
long to and are a 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 laya.’? On page 8, however, he says: 
“The rock occurs in two types, one not bear- 
ing 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 
diamantiferous.’? What is suggested by the 
difference between these rocks Lewis does not 
further indicate. He was mistaken as to the 
facts, as he afterwards appears to have learned. 
In his second paper, read in 1887, Lewis, in 
describing the mode of occurrence of the dia- 
monds, remarks.: 
“Tt is interesting also to find that they be- 
come more abundant the deeper they are from 
the surface, and where also the volcanic action 
was more intense. * * * * * 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 
they are not enclosures brought up from some 
other matrix.’’ He sums up the evidence as 
to the origin of the diamonds as follows: 
‘“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 
“kopjes’ from above, being mere alluvial de- 
posits, as held by Mr. Cooper and others ; after- 
wards, and until the present time, the idea has 
been general that they were carried up from be- 
low 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, 
SCIENCE. 
665 
hold that, while the serpentinous 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 be- 
yond question that diamonds are as much a part 
of the Kimberley rock as biotite, garnet, titanic 
and chromic iron and perovskite, and that, like 
these minerals, they may be considered as a 
rock ingredient. The fact that they continue 
just as abundant, if not more so, the deeper the 
mines are explored: that they are never found 
in, or especially associated with, the foreign in- 
clusions 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 color, lustre and shape, are, with 
the microscopical evidence of the eruptive char- 
acter of the rock, strong reasons for holding 
that the diamonds now lie in their original 
matrix.’’ This passage will bear but one inter- 
pretation and seems to represent Lewis’s final 
opinion. 
Later he refers to the fact discovered by Sir 
Henry Roscoe that the ‘blue ground’ contains 
a soluble hydrocarbon, but confines himself to 
characterizing this as a most interesting chem- 
ical observation. Lewis also presents Chaper’s 
results, according to which the rock of the 
Kimberley mines results from a series of erup- 
tions, between each of which there was time for 
the volcanic mass to consolidate, and in some of 
the mines it is possible to make out a chronology 
of the various eruptions. 
The only other passages pertinent in this con- 
nection are those referring to the occurrence of 
fractured diamonds. The fact that fragments 
of crystals are often found in the mine he ex- 
plains as due to the bursting of the diamonds on 
exposure to the atmosphere. He also notes, 
however, that many of the other porphyritic 
erystals of the kimberlite are broken. 
Whatever Lewis may have said in conversa- 
tion, his deliberately recorded opinion is that 
the diamond is a rock ingredient, as much a 
part of the rock as the garnet or the biotite. It 
cannot have been his wish to be represented as 
holding an opinion which, in these papers at 
least, he nowhere expressed, and from which he 
withheld his assent. 
