370 Revieics — Prof. H. C. Lewis — Genesis of the Diamond. 



and had in addition incorporated fragments of overlying rocks in its 

 upward progress." But he allows that this interpretation would not 

 necessarily affect his friend's views as to the genesis of the diamond, 

 VIZ., by the action of an extremely basic rock upon carbonaceous 

 material. 



Although there seems to be a pretty general consensus of opinion 

 that, in some way or other, a peculiar peridotite, invading carbon- 

 aceous beds, is tlae mother rock of the diamond, yet the evidence 

 at present is by no means conclusive either as to the depth or the 

 precise conditions under which this action took place. That 

 the diamonds originated lower down than the position in which 

 they are now found, is most probable, since the breccia in which 

 they occur is more or less of a mixture which has been forced 

 upwards. The evidence as to depth is somewhat contradictory ; 

 for, on the one hand, we haA^e the fact that the several pipes have 

 their own type of diamonds, a circumstance tending to indicate that 

 the diamonds originated in each pipe separately, and not in a general 

 reservoir. On the other hand, Ave have the fact that the area 

 within which diamond pipes may be expected to occur is of wide 

 extent, since the Leicester mine is forty miles from Kimberley and 

 Jagersfontein sixty miles. This might be held as pointing to a general 

 reservoir of diaraantiferous rock seated at a great depth. On the 

 whole it would seem that, although the peridotite may be widely 

 distributed, at a great depth, the conditions under which it becomes 

 diamantiferous are local and only occur in the pipes. 



The chemical aspect of the question, though not dealt with in 

 the present publication, has greatly changed since Professor Lewis 

 ■wrote. For many years chemists looked upon hydrocarbons as the 

 most promising material from which the diamond might have been 

 derived, and laboratory expei'iments were conducted on this 

 supposition. As bearing on this point, it is interesting to note that 

 Eoscoe by digesting the '' blue ground " with ether obtained 

 a hydrocarbon which was found to be crystalline and strongly 

 aromatic, burning with a blue flame and melting at 50° C. (p. 61). 



More recently, as is well known, Moissan and other chemists 

 have actually obtained small diamonds by melting iron mixed with 

 carbon in the electric furnace, and arranging the experiment so that 

 the separation of the iron from the carbon takes place under enormous 

 pressure. This reaction consequently is now regarded as the one most 

 likely to have produced diamonds in nature. " It is certain," said 

 Sir William Crookes, at a recent lecture before the Eoyal Institution, 

 "from observations made at Kimberley, corroborated by experience 

 gained in the laboratory, that iron at a high temperature and under 

 great pressure will act as the long-sought solvent for carbon, and 

 will allow it to crystallize out in the form of diamond — conditions 

 existent at great depths below the surface of the earth." 



Undoubtedly the fact that small diamonds have been made by 

 the action of iron on carbon favours the supposition that this, too, 

 may be Nature's process, and there is further corroboration in the 

 fact that iron-oxide is the most abundant substance of the ash of 



