Prof. T. Rupert Jones — Diamond Fields of S. Africa. 59 



talcose, and hornblendic schists, associated with it. (See the memoir 

 by MM. Heusser, Clarez, and G. Eose, " Annales des Mines," vol. 

 xlvii., 1860 ; translated in the Geologist, vol. iv., p. 168, etc., 

 1861.) This granular quartzose schist, and the other schists with 

 which it alternates,^ are extensively decomposed and readily washed 

 away in Brazil. They yield, besides the diamond, the minerals of 

 metamorphic rocks and their vein-stones, such as : — Quartz and 

 Amethyst ; Sulphur ; Euclase ; Kyanite and transparent Andalusite ; 

 Felspar ; Topaz ; Chrysolite ; Chrysoberyl ; Tourmaline, black, 

 green, and transparent ; Amphibole ; Hornblende ; Garnet ; Calcite 

 and Arragonite ; Specular Iron-ore and Haematites ; Magnetic and 

 Arsenical Pyrites ; Copper-pyrites ; Entile, Anatase, and Brookite ; 

 Ores of Tellurium ; Ores of Manganese ; Chromate of Lead ; Gold 

 and Platinum. 



In South Africa the abundance of agate in the gravel, leads us, as 

 above said, to see if the Karoo beds might be the original matrix of 

 the diamond there. The late Dr. E. N. Eubidge long since suggested- 

 that the influence of the many veins of volcanic rock, traversing the 

 plant-beds and coal of this formation, may have been a cause of the 

 reduction of the hydro-carbons to pure carbon ; and, though he could 

 advance no arguments in support, he could point to the change of 

 coal in the Stormberg into anthracite by that agency, and to the 

 existence of South- African graphite, possibly due to a further change 

 of the carbon in these rocks.^ 



Drs. Muskett and Atherstone, and perhaps Dr. Shaw and Mr, 

 Higson, seem to think, with Dr. Eubidge, that the Karoo beds, 

 or their dykes, are to be credited with the diamonds. But this 

 origin for the gem is left unsupported, except by Eubidge's sup- 

 position that, given coed altered to grapJiite hy heat, we may also have 

 coal altered into diamond ; and by the associated abundance of the 

 Karoo agates and the prevalence of the debris of Karoo strata in the 

 Vaal Valley (Griesbach). 



After all, as above intimated, the diamonds may either have been 

 native to the rocks out of which the Karoo deposits were largely 

 formed; or, more probably, they may have been derived from the 

 old rocks of the north-east, and from local outcrops of such rocks 

 in the Orange Eiver Free State itself. In this case agate and 

 carnelian are not the chief signs to be looked for in diamond- 

 yielding gravel, bixt an assortment of the minerals known to abound 

 in metamorphic rocks. 



1 Limestone also occurs witli these schists, which are thought by Agassiz and 

 Hartt to be probably Silurian rocks, highly altered. See also the Eev. G. J. 

 Nicolay's paper in the British Association Report, 1868 (Trans. Sect. p. 74), for 

 an account of one of the Brazilian diamond-iields. 



2 Quarterly Journ. Geol. Soc, vol. xi., p. 7 ; 1855. 



3 In the "Academy" for December, 1870, is an imperfect report of a discussion 

 at the Geological Society of London, wherein it is intimated that Prof. Morris ex- 

 pressed an opinion that, as the Bamboo produces tabasheer, so the Conifers of the 

 Karoo formation may have produced a resin that has since been converted into pure 

 carbon. We must wait for the elucidation of this hypothesis. See also Prof. Morris's 

 "Lecture on Diamonds," etc., Mining Journal, Dec. 17, 1870, p. 1063. 



