Prof. T. Rupert Jones — Diamond Fields of S. Africa. o3 



successful in discovering an immense deposit of ttie underlying rock 

 of the diamond region. It is a porphyritic gneiss, and no doubt lias 

 a very extensive range in South Africa. Mr. Hiibner showed me 

 specimens of the same fundamental rock, V7hich he had found 

 covering a large area of country to the north : it is the underlying 

 stratum at the Tatin and northern gold-fields, at the Chief Machin's 

 town, in the Bamangwato hills, and forms the great mass of the 

 Maquassie range of mountains in the Transvaal ; but Mr. Hiibner 

 had been unsuccessful in tracing it again after leaving the Maquassie. 

 Mr. Hiibner calls it a ' porphyritic granilite,' but I have rather ad- 

 hered to the nomenclature of Dr. Atherstone and others. My thus 

 finding the same underlying rock across the Yaal forms a connecting 

 link between the mineral regions of this part of the country, the 

 Transvaal, and the far interior.^ Proceeded about 16 miles down 

 the Vaal ; formations the same as before." 



Thus the Karoo strata continue not only up to the Vaal, but into 

 and beyond the Transvaal, and form considerable portions of the 

 region to the east, bordering on and forming part of Natal. In the 

 diamond-districts they have been worn down to a low level, in some 

 places, perhajDS, to the lowest crystalline rocks, at all events down to 

 the " Devonian" strata, which certainly come out to the hilly surface 

 further to the north-east, where Dr. Carl Mauch found specimens of 

 MurcMsonia in Sekhomos and Mosilikatzes country, in the Trans- 

 vaal Eepublic, in 1867. 



Of the well-known " Karoo Formation " itself, we may say that it 

 consists of an enormous series of shales and sandstones, rich at places 

 with the wonderful remains of extinct Reptiles {Dicynodon, Oudeno- 

 don, Micropliolis, Galesaurus, Cynochampsa, Massospondylus, Pachy- 

 spondylus, Leptospondylus, EusTcelesaurus, Orosaurus, Sawosternon, 

 Pristerodon, and others undescribed), and Palgeoniscan Fishes, to- 

 gether with Coniferous Trees, Ferns, and other Plants (among 

 which Lepidodendron has been noticed by Eubidge and Grey), 

 and coal-beds also. These strata are crossed by frequent trap- 

 dykes (doleritic?, dioritic, and syenitic) at different angles ; and 

 are often overlain by and intercalated with similar igneous rock. 

 Being horizontally bedded and much denuded, this extensive series 

 of strata constitutes table-lands and flat-topped hills, deeply divided 

 by broad valleys. A remarkable feature in this great series of 

 probably lacustrine deposits is its basement-bed of angular and 

 rounded blocks of trap, granite, etc., massed together in a dense 

 cement, which in some places appears to be felspathic, but elsewhere 

 argillaceous. Hence this great j)ersistent band has been variously 

 termed " claystone-porphyry " (Bain), "trappean conglomerate" 

 (Wyley), "a species of trachyte" (Sutherland), and "Boulder-clay" 

 (Sutherland and Griesbach). The late Dr. Eubidge thought that, on 



1 This "granilite" may possibly also be the same as Bain's binary granite of the 

 Paarl and near Bain's Kloof, not far from Cape Town. Geol. Trans., 2ud series, 

 vol. vii., p. 179. 



