106 Kepokt S.A.A. Ai)VAN('emknt ok 8cienck. 



A nionieiit's further inspection, howexer, showed that the kiths were 

 of calcite, though they had the peculiarity of extinguishing parallel 

 to their length. I think this greatly strengthens the inference that 

 the laths are pseudomorphs of the nielilite, especially when one con- 

 siders how unlikely it would be for calcite to completely replace any 

 other mineral in an ultra-basic rock. 



I may now turn to the interesting subject of the so-called eclogites, 

 of which fragments occur in most diamond pipes, including the newly 

 discovered ones near the Bembezi River in Rhodesia. Personally I 

 consider these rocks to be neither segregations from the Kiaiberlite 

 magma, nor even igneous rocks at all. Some, e.y. at the Roberts Victor 

 mine, contain kyanite and other metaniorphic minerals. Furthermore, 

 they occur i'li situ, sliowing every important feature of the fragments 

 from tlie pipes, in the Wankie and Tuli districts of Rhodesia, and are 

 obviously products of contact metamorphisni, garnetiferous pyroxene 

 granulites, in fact, forming part of the complex of mixed rocks occurring 

 at the junction of granites with highly basic .schists. These occurrences 

 have actually had large quantities of material from their decomposed 

 outcrops washed, but have yiehied no diamonds. 



Some have contended that the eclogites are the true source of the 

 diamond, and this seems to be accepted by Mr. Du Toit in his recent 

 account of the Kimberley district. I can scarcely understand this, as 

 the arguments against it are so strong. Blue ground or Kimberlite, or 

 whatever one terms the rock, is the inevitable matrix, t)nly two possil)le 

 exceptions being known in the closely related rocks of the Reiser mine 

 and of Inverell, N.S.W., and there is no reason wliatever why this 

 should be the case if eclogite were the real matrix. The eclogites ought 

 to be astonishingly rich in the gems if they were the source of the 

 diamonds in the blue ; Mr. Gardner Williams' test of twenty tons of 

 eclogite inclusions in the blue ground may therefore be considered 

 quite conclusive, as it did not yield a single diamond. 



Mr. Du Toit even suggests that the garnets. Arc, in the Kimberlite 

 originated from the churning up and disintegration of eclogite frag- 

 ments. But this is completely negati\ed by an observation which I 

 first made on the eclogite of the large Rhodesian pipe near the Bembezi 

 River, and which seems novel. 1 noticed that instead of being the 

 blood red pyrope, as in the blue ground itself, the eclogite garnets were 

 in every case of a yellowisli-brown tinge, and were obviously cjuite a 

 different \ ariety, similar to those so often found near granite contacts. 

 On examining fragments from Kimberley, the same fact was at once 

 apparent, and when it is remembered that the garnets in the blue are 

 almost without exception pyrope, T think we may dismiss from con- 

 sideration any such ideas as their derivation from churned up eclogite. 

 Indeed, 1 think that it is quite sufficient to ilisprove also tlie theory thai 

 the pipe diamonds come from eclogites at all. 



