GEOLOGY OF THE SOUTHERI* TRANSVAAL. 457 



In view of tho great peraistonco of certain beds over large areas 

 in this region, I am inclined to think that, as already stated, the 

 anriferons conglomerates of the Devil's Kantoor, and tlie chalcedo- 

 lites of the lilyde lliver and elsewhere in the Lydenbnrg district, 

 establish the position of the rocks of that district as part of tho 

 upper series of tlie ^Ipgaliesberg formation. They need not again 

 be described ; but it may be repeated that " the chief exposure of 

 the chalcedolites is along the Blyde River, best seen on its western 

 side or escarpment, where the rock occurs in two series," as it does 



near Pretoria, " the lower several hundred feet in tliickness 



It contains fine gold in places, and, where in a decomposed state, 

 it has been worked as so-called * rotten-reef ' to a considerable 

 extent '' *. 



As previously mentioned, the De-Kaap-Yalley beds are faulted, on 

 both the north and the south, against the granite, the lines of fault 

 probably coming together in the region to the eastward. In a 

 similar manner the whole of the lower half of the Megaliesberg 

 formation is let down against the north side of the granite S. of 

 Pretoria, and against its east side by a fault at nearly right angles 

 to tho former. Another line of fracture branches off to the east, 

 bringing the upper half of the formation directly against the lower, 

 but with a possible intrusion of trap-rock along the line ; the geo- 

 logy hereabouts is, however, very obscure, and the tilted rocks soon 

 pass in under the newer formation of the next section. I am in- 

 clined to the opinion that the Pretoria E. and W. fault extends even 

 down to Klerksdorp (across a district at present unknown to 

 me), where, as in the preceding instance, the upper series abuts 

 directly against the lower, as shown in the section (PI. XY. fig. 1). 

 Also, that another E. and W. fault will be found to occur north of 

 Pretoria, letting down the beds that form the Megaliesberg Range 

 against the granite which is known to appear at the surface not 

 very far north of the mountains. 



III. The High- Veldt Coal-formation. 



The newest formation of all here is that which I described in 

 1884 as the High-Level Coal-fields of South Africa t. It rests 

 unconformably upon the older rocks, and, with local exceptions, 

 very nearly maintains its original horizontality. Some important 

 coal-seams are now known to be continuous for many miles ; and I 

 feel still more convinced of the lacustrine origin of coal. 



The " Kimberley Beds " (g) make up the lower portion of this coal- 

 formation on the west, but thin out eastwards, and are overlapped 

 near Klerksdorp by the " High- Veldt Beds" (cj) or upper portion, 

 the estimated thickness of which is 2300 feet. The amygdaloidal 

 dolerite (/) upon which the " Kimberley Beds " rest, and which is 

 met with at a depth of 300 feet in the Kimberley Diamond Mine, 

 has now been traced eastwards to a great distance. It crops out at 



* Op. c-it. (1885) p. 577. 



t Quart. Journ. Geol. Soc. vol. xl. p. 658. 



Q. J. G. S. No. 187. 2 1 



