496 Trof. Bonney and Miss Raisin — Roclisfrom Kimherleij. 



(II) On the Eock and other Specimens from the Kimberlet 



Mines. 



By Prof. T. G. Bonney, D.Sc, LL.D., F.E.S., and Miss C. A. Raisin, B.Sc. 

 rpHE undecomposed rock is obviously a fairly hard breccia, 

 I exhibiting a rather irregular fracture and consisting of minerals 

 and rock fi-agments in a blackish-green, slightly granulated " paste." 

 Some of the minerals, probably fragments, can be readily identified, 

 e.g., olivine, green pyroxene, brown mica, and garnets. The frag- 

 ments of rock are of various sizes up to about tvs^o inches diameter. 

 They are generally rather compact in texture, greenish-grey in colour, 

 sometimes exhibiting a zonal structure near the edges. The specific 

 gravity, determined by a Walker's balance, of a specimen of the 

 breccia measuring about 2J" x 2" x |" is 2-61 ; of a piece about 

 one-fourth that volume, 2-66.^ 



Under the microscope the rock is seen to consist of fragments 

 large and small, becoming at last a mere powder, which are set in 

 a serpentinous mineral and a carbonate, these acting as the cementing 

 paste, but the latter mineral being more sporadic in occurrence. 

 Commencing with the larger minerals- in the specimen before us, 

 (1) Olivine is the most abundant. Its cleavage in some cases is 

 a little more marked than usual. It occurs generally in rounded 

 grains, partially ringed by serpentine, indeed sometimes completely 

 converted into this mineral. Tlie alteration usually is as follows : — 

 Eound each grain is a zone of fibrous serpentine, exhibiting a rather 

 parallel ordering, which acts feebly on polarized light. A zone 

 follows where the fibres are arranged in cones, the apices of which 

 seem to pierce the olivine, as if the cone structure had gradually 

 extended inwards and had afi^ected indirectly that of the whole 

 layer. Here, however, the axes of the cones are more or less 

 parallel. This parallelism seems to depend on some structure in 

 the olivine itself — most probably a cleavage — and not on the form 

 of the grain. In some cases the fibrous mineral seems, from the 

 extinction angle, to be actinolite or tremolite.'' 



(2) Sahlite, or lightish-green augite, occurs in grains often somewhat 

 oblong, commonly with an alteration zone at the exterior, consisting 

 of a fibrous mineral, which has the extinction of actinolite. The 

 olivine and the sahlite often present considerable resemblances in 

 their general microscopic aspect, and the same holds true of their 

 alteration products. 



taken place in the appearance of the strata. We have now passed through some 

 200 feet of this formation, and I am in hopes of getting a change which will be 

 very interesting." Mr. Moses also promises to send a fui-ther box of samples 

 when this takes place, which it is needless to say will be of additional interest 

 nnder the circumstances. 



' These specimens were given to one of the authors by C. J. Alford, Esq., F.G.S. 

 That brought by Sir J. B. Stone was inconveniently large for weighing. 



2 A number of analyses of minerals are given in the paper by Prof. Maskelyne 

 and Dr. Flight, Quart. Jom-n. Geol. Soc, vol. xxx, 1874, pp. 408-416. In our 

 specimens, bronzite, which appears to be common in their material, seems to be rare, 

 if not absent. 



3 As was also observed by Prof. Carvill Lewis. 



