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



torrents have, in relatively late times, supplied mncli of tlie agate 

 that now coats the flats of the great valley, or if an old alluvium ^ 

 has been re-sifted and reduced to lower levels, or if the degradation 

 of the rocks in place during immense periods of time has left the 

 agate gravel of the Free State, are open questions.^ Again, has this 

 degradation been due to atmospheric and pluvial action (Eubidge, 

 etc.), or mainly to glacial action, as recently advocated by Mr. G. W. 

 Stow ? In either case, whether the diamonds and other minerals 

 have come out of granite, palaeozoic schists, or Karoo beds, even if 

 they have been brought from some distance, they may have come 

 without damage in the glaciers and the river-ice, or they may have 

 been freed from their travelled matrix by subsequent degradation. 



But what was their original matrix, and where is it to be sought 

 for? If it be granite, that rock is still to be found, perhaps in 

 local outcrops, and certainly not far up the Vaal, above Potscherfs- 

 troom ; although the old granite shores bounding the Karoo forma- 

 tion have long since been worn down to lower levels even than 

 those of the deposits once formed of and within them. Plentiful 

 wrecks, however, of the old granite are contained in the Karoo beds, 

 and often exposed, as before said. 



If among gneissic, micaceous, talcose, argillaceous, or other schists 

 the matrix of diamond is to be looked for, we are not without in- 

 dications of the existence of such old altered rocks, together with 

 marble, in and about this region ; for they are not wanting on the 

 north side of the Vaal and Orange basin ; and they are all usually 

 associated with granite more or less intimately.^ 



That some old schistose rocks contain diamonds in Brazil is well 

 known, especially the granular quartzose rock, called " itacolumite" 

 (sometimes flexible*), and certain argillaceous, micaceous, chloritic, 



side of the continent. As diamonds are associated with the ruins of such rocks in the 

 upper part of this great river's course, possibly they may be found among the 

 detritus of the same rocks crossed by it near its mouth. As Dr. Sutherland has 

 shown that old crystalline palaeozoic, and Karoo rocks are all denuded together in 

 Natal, probably among their ruins diamonds are to be found in that country also. 



^ For Dr. Eubidge's views respecting the eastern source of the agates, and of the 

 old high-level flats and terraces of agate gravel, see Geol. Mag., Vol. III., p. 89. 



^ Dr. John Shaw (" Nature," Nov. 3, 1870) thinks that "a series of metamorphic 

 and sedimentary rocks which lay above the present rock-system of the region," have 

 been slowly worn down; the shifted and reduced debris, and a few local remnants of 

 the series, being all that remain of these old rocks, which he thinks may have been 

 the original seat of the diamonds. Dr. "W. G. Atherstone says (Geol. Mag., No. 

 59, p. 212) : — " From the great distance of the finding-places apart, and their pro- 

 pinquity to the several river-beds, which all proceed from the Quathlamba or 

 Draakenberg sandstone ranges, I have little doubt that, on careful exploration, 

 the real source of the diamond deposits will be found far to the eastward." 



3 The finding of diamonds at Bloemhof, near Potscherfstroom, if well substantiated, 

 is of great importance in our inquiry; for it shows that the presence of the Karoo 

 beds is not necessary for their occurrence; since the Karoo formation does not reach 

 so far, according to Mr. Higson's observations (" Natal Herald," August 8, 1867). 

 In this case they must have come from the metamorphic or the granitic rocks of the 

 Transvaal, as the drainage of the Magaliesberg, with its Karoo beds, goes northward. 



* The flexible itacolumite (or sandstone of quartz and rotten felspar), associated 

 with diamond-fields in India, is found beyond the Draakenberg, in Natal ; and there 

 it is accompanied with a kind of jade, as in Siberia. 



