I'l'.f. T. <:. IJonney. <> BotUder* and other Bock Specimen* 



of a rlull white colour, -peckled with green, are present. Mil TO-, pic 

 examination shows that the larger minerals do not call for any special 

 notice, except that a rudely . rcscentic pyrope has a kelyphite rim on 

 tin- <-onrave as well as on the convex side, proving the fracture to !* 

 an old one. Hut the small plates of a In-own mica, the occurren, e of 

 whid) ha- lieen already noticed,* are very abundant in the matrix. 

 These plates in some of the specimens are rather irregularly outlined, 

 and rarely exceed O'OOl inch in diameter. Init in others they average 

 alout doulile that si/,e, and occasionally a few of them may even < 

 Q-004 inch. Then the outline is more, rectangular, and the cleavage 

 more distinct. The smaller flakes often tend to form a /.one around 

 included rock fragments, and scattered granules of iron oxide 

 more common in the .-li--e- containing the larger flakes. t I have now 

 no douht that the miner;*! is a secondary product. 



The unusual abundance of a minute brown mica in the ground mas- 

 made an analysis desirable. For that annexed T am indebted to Mr. C. 

 .lames, who has executed it in the laboratory at T'niversity College 

 under the supervision of Professor AY. 1 tarn say. 



Silica 3S-77 



Alumina 14'62 



Ferric oxide 11-36 



Calcium oxide 4-."Jl 



Magnesia 12-14 



Potash 2-63 



Soda 1-90 



Loss on heating CO^ and H/J 1 >'>') 



99-4S 



(The iron was all estimated as Fe-jOsj one specimen gave a trace of 



nickel.) 



If we compare this analysis with one given by Professor C. Lewi's.; 

 SiO 2 = 33-00, FeO (including Al.O 3 ) = 12-00, MgO = 32-3S, CaO = 

 0-63, Xa..-O = 0-67, CaCO 3 = 16-02, H,.O = 6-0 (total 101-71), and 

 with those of Kentucky " kimberlites " <iuot<xl by Rosenbus. h.^ and 

 by Lewis,|| we see them to be poorer in alumina and alkalies, but 

 richer in magnesia. Serpentine, in fact, forms the dominant silicate 

 in them, a ferro-magnesian mica in this, the other mineral not amount- 

 ing at most to a quarter of the whole rock. But we must remember 



* 'Geol. Mag.,' 1897, p. 151. 



t In all thcM- >p*'i-imens from >Y\vlaniU opaque granule* (? ilim-nitc) vein to 

 lake the place of the translucent brownish granules (in part pcrof-kite) in the 

 spec-linen- frm De Beers Mine. 



J ' The Matrix of the Diamond.' p. 17. 



' Kleineute dcr Cotein-lchre,' p. 165. 



,| 'The Matrix of the Diamond,' p. d, ;/*. p. >1. 



