Mr. Bain on the Geology of Southern Africa. • 189 



morphosed for a distance of 40 or 50 yards, and sometimes converted into perfect 

 hexagonal columns. Tiie slaty rocks likewise, which are within its influence, from 

 being of a dark blue colour, have been changed to black, much resembling in 

 appearance fine-grained basalt. There are many smaller dikes in various parts of 

 the country, protruding through the sandstone in a similar manner, and shaped like 

 the Spitzkop. These also, being harder than the horizontal strata, have longer 

 withstood the action of the elements, which have disintegrated and worn away 

 the softer sedimentary deposits. 



I have endeavoured to show some of the principal dikes in the sections, but 

 have not attempted it in the map ; for, without a proper survey of the whole 

 country, even an approximation to the truth could not be attained, as the dikes 

 appear to run in every direction, forming an irregular network, which would only 

 disfigure the map, and look like a confused mass of roads*. 



Having now briefly, though very imperfectly, sketched the different formations 

 of South Africa, and to the best of my ability laid down the same on my map and 

 sections (PI. XX. XXI.) in such a manner as, I trust, will be intelligible, it will 

 be seen that I have been so far successful in tracing at least a part of the Dicyn- 

 odon's habitat, with that of the other wonderful reptiles with remains of which 

 my collections abound. The existence of a great lake or inland sea, occupying 

 the major part of the South African promontory, was never once dreamt of by me 

 when I first discovered those singular rehcs, but subsequent researches have con- 

 vinced me that such was the case, and moreover that the period of its existence 

 was shortly after the deposition of what I have called in this sketch the " Carboni- 

 ferous formation," the " claystone-porphyry " only intervening between it and the 

 Reptiliferous deposits. I have arrived at the conclusion of the lacustrine origin 

 of this extensive area from the fol.owing facts, viz. : — 



1st. The general uniformity and homogeneity of the deposits. 



2nd. The great abundance of fossil wood, and the similarity of the vegetable 

 remains found throughout the range of these beds. 



3rd. The large quantity of freshwater plants traversing the strata in the vertical 

 position on the spot where they grew. 



4th. The peculiar characters of the reptiles found fossil in these strata, and 

 unknown elsewhere. 



5th. The general absence of marine exuvise, and the presence of small fresh- 

 water shellsf. 



* See also Capt. Charters's observations on the vast extent of greenstone in South Africa, Proc. Geol. 

 Soc. vol. iii. p. 102.— Ed. 

 f Mr. Bain's collection does not afford certain evidence on this point. A piece of rock with minute 



