1899] THE SOUTH AFRICAN DIAMOND 181 



eclogite, as a zircon is of a granite or syenite. It may prove, how- 

 ever, not to be restricted to this one species of rock. I see no reason 

 why it should not also occur in the enstatite-eclogite already described ; 

 while the fact that at Kiniberley, if not at Newlands, olivine is 

 abundant in the diamantiferons blue ground suggests the possibility 

 that the diamond may also be a constituent of a peridotite. In fact, 

 though I was unable to accept my late friend Professor Carvill Lewis's 

 view that the Kimberlite was an altered peridotite, I fully expected 

 that sooner or later it would be traced back to some very basic rock, 

 probably to a peridotite. The diamond hitherto has only been proved to 

 occur in meteoric iron 1 (Canon Diablo), and it was made artificially 

 by Professor Moissan by the intervention of that metal. Indeed, on a 

 priori grounds I should have expected to find it in a rock less acid than 

 an eclogite. I venture, accordingly, to suggest that the crystallisation 

 of the carbon may possibly have occurred in some very basic magma 

 which was afterwards invaded by one more acid, the eclogite being the 

 result of the mixture. This, however, is a speculation ; the fact, I 

 think, cannot be disputed that the diamond has been traced back to an 

 igneous rock (eclogite) and was not formed in the " blue " (Kimberlite). 



The boulders described above appear to me truly water- worn ; so also 

 are not a few of the smaller fragments. I suspected this some time 

 ago when examining a parcel of " washings " from the De Beers Mines 

 (where also boulders have occurred), but those sent to me from 

 Newlands have placed it beyond doubt ; half a small pebble of 

 eclogite is present, while many of the minerals are so well rounded 

 that the darker kinds could only be determined by fracture. But if 

 this be so, if many of the constituents are water-worn, how can the 

 so-called Kimberlite be an altered porphyritic peridotite ? We are 

 compelled to regard it as a clastic rock, formed by explosions, which 

 have mingled the shattered constituents of the coarsely crystalline floor 

 with materials derived from the overlying sediments. The comparative 

 abundance of diamonds in the blue ground suggests that they are fairly 

 common in some members at least of the holocrystalline series. Hence 

 it may be possible, by carefully observing the larger minerals found 

 with diamonds, to infer which of them are really its associates. At 

 present, garnet, chrome-diopside, and perhaps iron oxides, can alone be 

 named, but I fully anticipate other pyroxenes and olivine to be added. 



Hence, as the blue ground is not an altered peridotite, the 

 name Kimberlite must be removed from the list of that group, and 

 must disappear from science, unless it be retained for this peculiar 

 breccia in which the diamond very commonly is an accidental con- 

 stituent. The mode of occurrence, structure, and contents of this 

 breccia suggest that it is the result of some kind of volcanic action, but 

 the general abseuce of scoria makes it probable that the explosions were 

 due to accumulated steam, and were thus of an exceptional character. 



1 The Novo Urei meteorite, however, is said to contain some ferro-magnesian minerals. 



