174 THE ORIGIN AND FORMATION OF THE DIAMOND. 



Operandi ? To begin with, whence came the carbon necessary 

 lor the formation of the diamonds, and in what form was it ? 

 We ran only enumerate such sources of carbon as we know actually 

 exist in the mines, but of course other sources may previously 

 have existed, the evidence of which is now lost. The possibility 

 of the carbonaceous shales supplying the carbon has apparently 

 been put asicfe by the South African geologists, on the ground 

 that some diamond mines evince no trace of having been overlaid 

 by the shales. The known possible sources of carbon then are ; 

 firstly, carbon dioxide and carbonates. Carbon dioxide is known 

 to be abundantly given off from volcanoes in the solfatara stage, 

 besides being freely evolved from the mud volcanoes that exist 

 on a small scale at the present day. It has been found, as 

 I have mentioned, in the liquid condition in the cavities of some 

 diamonds, and also in other minerals. It occurs in the form 

 of carbonates both in the blue ground itself and in the secondary 

 veins within and outside the mines. If not derived from the 

 decomposition of other carbonate "> deep down in the mines, it may 

 be assumed to be derived from the decompo ition of carbonaceous 

 materials that previously existed in the mines, and therefore, to indi- 

 cate the possible existence of such materials at a stage when the mines 

 were in their heyday of activity. Some years ago traces of hydrocar- 

 bons were found by Sir Henry Roscoe in the blue ground from Ue 

 Beers, and recovered by treating the powdered blue with ether and 

 evaporating. We must, I presume, suppose that this hydro-carbon- 

 aceous substance was present in the blue at the time it solidified. 

 For myself, I think that it may originally have been derived 

 from pieces of shale that were always falling into the open mines 

 before their final cessation of activity. This shale is, and no 

 doubt then was, decomposable, as is shown by its decomposition 

 when exposed to the weather. At one time^ before the mines 

 had got below the horizon of the shales trouble was caused by 

 such decomposition, which on one occasion led to an explosion 

 of marsh gas liberated from the decomposing shales. This 

 decomposition of the shales may also have been the source of the 

 paraffin which Sir William Crookes says is sometimes found in 

 the Kimberley well water ; and, which, when it occurs in the 

 mines, Sir William ascribes to his heated masses of iron when 

 acted on by water or steam : but, which, I submit, may have 

 this less far-fetched explanation. 



Mr. Crardner Williams mentions another deep shaly rock, lying 

 below the quartzite, which seems to contain organic matter. But 

 the blue ground itself contains a minute proportion of carbon, 

 in the form of graphite, mixed with minute diamonds. When 

 it is taken, powdered, and acted on by acids to dissolve the mineral 

 constituents, a little insoluble residue, consisting of minute 

 diamonds and graphite, is left behind. This is a most interesting 

 fact, as showing that the graphite is fairly evenly distributed 

 throughout the blue. Graphite has been found grown into 

 the diamonds themselves as I have previously mentioned. The 

 relation of this graphite, when present in diamonds, to the dia- 

 monds themselves. I will consider later. 



