THE GEOLOGY OF THE SOUTHERN TRANSVAAL. 451 



25. A Contribution to the Geology of the Southern Transvaal. 

 By W. H. Penning, Esq., F.G.S. (lload February 2.3, 1891.) 



(Abridged.) 



[Plate XV.] 



Contents. 



Page 

 I. Introduction 401 



(</) The Southern Transvaal. 



\b) The De-Xaap Valley and NorLhern Swaziland. 



II. The Mecjaliesbeiig Formation 452 



(rt) The Witwatersrand Series. 

 {hi) The Klip-River Series. 



III. The High-Veldt Coal-formation 457 



IV. Denudation 459 



(«) Before the High-Veldt Coal-formation. 



(h) Of the present surface. 



(c) During the early part of the High-Veldt Coal-formation. 



I. Introduction. 



(a) The Southern Tratisvadl. — The area occupied by the "Wit- 

 watersrand beds offers many facilities for accurate observation. I 

 have been enabled to collect sufficient evidence to fairly establish 

 the relation between the geology of the district and that of the older 

 known gold-fields, and thus to briefiy describe the geology of the 

 Southern Transvaal*. The accompanying map (PI. XV.) shows an 

 area about 350 miles in length and 50 miles in breadth (or 17,500 

 square miles in extent). Some points require further elucidation ; 

 but the geological features, as expressed on the map and sections, 

 are generally correct according to my interpretation. 



For a description of the district here referred to and its eastern 

 border, see Quart. Journ. Geol. Soc. vol. xl. (1884) pp. 658 et seqq., 

 with map and sections. 



The granitic rocks are most frequently fine-grained, and generally 

 include little mica, but sometimes much hornblende. AVhether 

 pegmatite, syenite, or granite, they are comparatively little exposed 

 in the Southern Transvaal. 



The granite (a, on map and sections) is frequently broken through 

 .by dykes of diorite, which almost always run nearly north and 

 south. So also are the stratified rocks of all ages broken through in 

 this way ; but the older these are the more numerous are the dykes 

 within them. In the granite, the various minerals have sometimes 

 been re-assorted by the effects of the dykes — layers of quartz and 

 felsite, or of kaolin, flanking the dykes on both sides for consider- 

 able distances. 



* Quart. Journ. Geol. Soc. vol. xli. (1885) pp. 569, &c. 



