Walcot Gibson — PalcBOzoic Rocks of South Africa. 211 



Beds, Dr. Molengraaff arranges them in the following descending 

 groups : — 



Table of Strata below the Beaufokt Beds of the Transvaal.' 



Karroo ( Ecca Series ... ... ... Shales and diabases. 



System. ( Dwyka Conglomerate ... ... A coarse conglomerate of variable 



composition and of glacial origin. 

 Great Unconformity. 



Amygdaloid Rocks of the Boschveld (age doubtful). 



Cape 

 System. 



/'Waterberg Sandstones 



Plutonic Series of the Boschveld 



Pretoria Series ... 



Dolomite Series .. . 



Black Reef Series 



Primary 

 South 

 African ' 



System 



Great Unconformity. 

 Amygdaloid Rocks 



Ancient Granite Series 



Barberton, Hospital Hill, and 

 Witwatersrand Series 



Sandstones, breccias, conglomerates, 



diabases. 

 Porphyroids, red granites, norites. 

 Shales, quartzites, diabases. 

 Cherts and dolomites. 

 Sandstones, quartzites, shales, and 



conglomerates. 



Diabases, amygdaloidal lavas, por- 



phyrites. 

 Grey granite. 



Schists, quartzites, gold-bearing 

 conglomerates (Banket) . 



This table embodies the results obtained by Dr. Molengraaff 

 during several excursions undertaken in the years 1898 and 1899 

 with the object of a future systematic study of the region, and is 

 by far the most complete of any yet produced. Dr. Molengraaff's 

 classification differs from nearly all others by including the Banket 

 formation in the Primary South African System,- instead of con- 

 sidering it to be the northern equivalent of the Table Mountain 

 Sandstone. Dr. Molengraaff further differs from many observers 

 in regarding the granites and gneisses cropping out between 

 Johannesburg and Pretoria and round Vredefort as intrusive into the 

 Hospital Hill Series, whereas they have generally been considered 

 to belong to a much older Archaean massif in which the gold-bearing 

 rocks have been enfolded by earth - movements. Which view is 

 correct can only be satisfactorily determined by systematic mapping. 

 In the meantime it is of more service to draw attention to the results 

 obtained in mining and especially from an examination of the area 

 immediately round Johannesburg, of which considerable information 

 has been obtained of late years. 



Soon after the commencement of the gold industry the auriferous 

 rocks were believed to be arranged in a unicline, comparable with 

 an English coal-basin. In 1892 it was shown, ^ chiefly from 

 observations from surface outcrops, that overthrusting had taken 

 place to a considerable extent, possibly disguising the succession 

 and certainly causing much repetition. Since then the progress ot 

 mining, and especially the development of ' Deep Levels,' has 

 conclusively proved the existence of several overthrust faults of 

 considerable vertical displacement, resulting in the duplication at the 



1 Dr. G. A. F. Molengraaff : Bull. Soc. Geol. France, 1901, ser. iv, t. 1. 



2 See also W. Gibson : Geol. Mag., Dec. IV, Vol. IV (1897), pp. 548-550. 

 ^ W. Gibson: Q.J.G.S., vol. xlviii (1892), pp. 404-437. 



