Yol. 54.] WITWATEESEAND AND OTHEK DISTEICTS IN S. TEANSVAAL. 77 



I am inclined with Molengraaff^ to separate the formation into an 

 Upper and a Lower Division ; hut whereas he puts the division 

 between the dolomite and the Black Eeef, I include the latter and 

 the underlying Klipriversherg amygdaloid in the Upper Division 

 namely : — 



C Magaliesberg and Gatsrand Series. 



Upper Beds, < -r,, i t> ' c j 

 Black Keer and 



[ Klipriversberg Amygdaloid. 



T TD f Witwatersrand Beds. 



Lower Beds. -^ ^ ., , ttii o • 



[ Hospital Hill feeries. 



1. The Hospital Hill Seeies. 



This series has been variously named. It is the ' Schistose 

 Eocks ' of Alford,^ the ' Lower Q,uartzite-and-Shale Group ' of 

 Gibson,^ and the ' Alte Schieferformation ' of MolengraafF.* 



Its typical occurrence is in the hill-range on which the Johannes- 

 burg Hospital stands, and generally known as Hospital Hill. The 

 formation invariably goes by this name locally ; and the term 

 clearly indicates, without chance of confusion, the beds to which it 

 is meant to be applied. 



Distribution. 



This formation consists of four or five alternating series of 

 quartzites and shales, the former, as a rule, cropping out on the hill- 

 ridges and the latter in the valleys. Its outcrop measures 3 to 

 6 miles across the strike. The east-and-west hill-range, on the 

 southern flank of which Johannesburg is situated, runs north of the 

 Main Eeef Series of conglomerates from near Boksburg to Krugers- 

 dorp, a distance of 45 miles. The dip of the beds is southerly, 

 mostly at a high angle ; in places the beds are even vertical at the 

 outcrop. West of Krugersdorp the strike changes to the south-west, 

 the new direction being maintained for about 20 miles until the beds 

 disappear under the unconformably overlying dolomite near Wonder- 

 fontein. The same beds reappear at a point about 10 miles west 

 of Frederikstad, whence they run in a well-defined hill-range 

 striking south-west past Buffelsdoorn and on to Xlerksdorp, the dip 

 of course being to the south-east. East of Johannesburg the 

 Hospital Hill Series can be traced to Klipfontein, about 12 miles 

 north-east of Boksburg, where it disappears under the dolomite. It 

 is next found at Boschmanskop and Vlakfontein, some 10 miles 

 north-west of the Nigel, and is there striking nearly due south and 

 dipping west. It is apparent therefore that, while hidden by the 

 Dolomite and the coal-beds of the Karoo Formation, the strata of 

 the Lower Cape Formation have swerved round to the south — an im- 



1 Neues Jahrb. Beilage-Bd. ix (1895) p. 209. 

 ^ ' Geological Features of the Transvaal,' London, 1891, p. 5. 

 3 ' On the Geology of the Gold-bearing & Associated Eocks of the Southern 

 Transvaal,' Quart. Journ. Geol. Soc. toI. xlviii (1892) p. 420. 

 * Op. swpra cit. p. 194. 



