572 Reports and Proceedings. 



The author described the general structure of the region in -which 

 diamonds had been found. He considered that the diamonds origi- 

 nally belonged to some metamorphic rock, probably a talcose slate, 

 which occupied the heights during a late period of the '' trappean 

 upheaval," to which he ascribed the origin of the chief physical 

 features of the country. This upheaval was followed by a period of 

 lakes, the traces of which still exist in the so-called " pans " of the 

 region ; the Yaal river probably connected a chain of these lakes ; 

 and it is in the valley of the Vaal and the soil of the dried-up 

 "pans" that the diamonds are found. The author referred also to 

 the frequent disturbance and removal of the diamantiferous gravels 

 by the floods which prevail in these districts after thunder-storms. 



3. " On the Diamond-gravels of the Vaal Eiver, South Africa." 

 By G-. W. Stow, Esq., of Queenstown, Cape Colony. Communicated 

 by Prof. T. Eupert Jones, F.G.S. 



The author described the general geographical features of the 

 country in which diamonds have been found, from Mamusa on the 

 south-west to the headwaters of the Vaal and Orange Eivers. He 

 then indicated the mode of occurrence of the diamonds in the gravels, 

 gravelly clays, and boulder-drifts of the Vaal Valley, near Pniel, 

 including Hebron, Diamondia, Cawood's Hope, Gong Gong, Klip 

 Drift, Du Toit's Pan, and other diggings. By means of sections, he 

 showed the successive deepenings of the Vaal Valley and the gradual 

 accumulation of gravel-banks and terraces, and illustrated the enor- 

 mous catchment area of the river-system, with indications of the 

 geological structure of the mountains at the headwaters. The speci- 

 mens sent by Mr. Stow, as interpreted by Prof. T. E. Jones, showed 

 that both igneous and metamorphic rocks had supplied the material 

 of these gravels. The author concluded that a large proportion of 

 these materials have travelled long distances, probably from the 

 Draakensberg range; but whether the original matrix of the dia- 

 monds is to be found in the distant mountains or at intermediate 

 spots in the valleys, the worn and crushed condition of some of the 

 diamonds indicates long travel, probably with ice-action. Polished 

 rock-surfaces and striated boulders, seen by Mr. Gilfillan, were 

 quoted in corroboration of this view. 



Discussion. — Mr. Henry "Woodward mentioned that Mr. Griesbach, who was 

 present, informed him that his fellow traveller, Mr. Hiibner, had been over the 

 country described in these papers, and had communicated a map and a paper thereon 

 in July, 1870, to Petermann's Journal. 



Mr. Griesbach stated that the rock described as metamorphic in the paper was by 

 M. Hiibner regarded as melaphyre, and that in some parts of the Vaal valley the 

 beds of the Karoo formation might be seen in situ. He disputed the possibility of 

 any of the gravels being of glacial origin. He was convinced that there were no 

 metamorphic rocks on the western side of the Draakensberg ; those regarded as such 

 probably belonged to the Karoo formation. 



Prof. Tennant commented on the large size of the diamonds from the Cape, of 

 •which he had within the last few months seen at least 10,000, many of them from 

 30 to 90 carats each. Some broken specimens must, when perfect, have been as 

 large as the Koh-i-noor. 



Mr. Tobin corroborated the information given by Mr. Stow, and stated that the 

 source of the Vaal was in sandstone, and that it was not until it had traversed some 

 distance that agates, peridot, and spinel were met with. The large diamonds, in his 



