•172 THE ORIGIN AND FORMATION OF THE DIAMOND. 



ihv Dumont, otherwise the simultaneous presence of graphite and siUcates, 

 with protoxide iron bases, such as mica, hornblende, &c., would certainly 

 I'lave given rise at least to a partial production of metallic iron." 



,;,Siich reasoning, I submit, would only hold good in the absence 

 of water ; in its presence, and it almost certainly was present, 

 the iron would be re-oxidised again to the black oxide, with 

 liberation of hydrogen. 



,:..In the case of diamonds found in eclogite some of them have 

 evidently .crystallised on the garnets and taken the form of the 

 latter. As garnets can be meltvcd at a full red heat, at least 

 ;thpse containing oxides of iron, we must assume in the case of 

 dianjpnds found crystallised on them and taking their form, 

 th^t such diamonds, in the course of their formation, could 

 not have been exposed to a temperature sufficient to have melted 

 the . garnets on which they were crystalhzing. 

 .^.:It is often stated that diamonds and garnets must have had 

 a similar origin because they are often found together, and we 

 find such authorities as Professor Bonney. Mr. Waldemar Lindgren, 

 ape} others, declaring eclogite and other garnetiferous rocks to 

 be the matrix of the diamond. It is true that, where diamonds 

 are found, there also you will generally find garnets, but the 

 converse does not hold good, as there are hundreds of localities 

 all over the globe where garnets are found that are destitute of 

 diamonds, even where carbonaceous materials are also present. 

 As regards the presence of abundant garnets in the pipes 

 of the South African Diamond Mines it must be assumed that 

 they were formed in the blue ground, as no sufficient source of 

 such a quantity of garnets has been found in the adjacent rocks. 

 Their formation in the pipes is quite analogous to what we know 

 of their formation in many parts of the world where local and 

 regional metamorphism has prevailed. 



Some diamonds contain angular fragments of other minerals. 

 The angular character of these latter shows that the diamonds 

 containing them could never, during their formation, have been 

 exposed to a temperature sufficient to melt those foreign en- 

 closures. One diamond is recorded as containing a piece of 

 gold leaf. Some are said to have been found containing bituminous 

 materials. Others undergo a change of colour on heating, and 

 it is supposed that their colour in that case is due to some organic 

 compound ; or, if not, then due to a hydrated compound, 

 such as oxide of iron, which becomes dehydrated on heating. 

 This idea gains some credibility from the fact that some diamonds, 

 which on heating change their colour, gradually regain it again 

 on cooling. 



..The presence of most, if not all, the foreign inclusions in dia- 

 monds that I have enumerated would seem to prove conclusively 

 that the diamonds containing them could not have been formed 

 at. .a very high temperature. 



Regarding the production of diamonds from molten iron, I 

 think that the facts I have mentioned are on the whole destructive 

 of that theory, but I will now mention some others that I have 

 long considered are antagonistic to it. Let us take the relative 



