YoL 54.] WITWATERSRAND AND OTHER DISTRICTS IN S. TRANSVAAL. 87 



recognized as a dolomitic limestone by A. Schenck/ who noted its 

 widespread occurrence, mentioning it near the Magaliesberg, in 

 Bechuanaland, the Western Transvaal, the Drakensberg, and Great 

 Namaqualand. Penning^ called it chalcedolite, and described it as 

 a calcareo-siliceous rock with ' chalcedonic texture'; and Alford' 

 described it as a ' calcareous quartzite . . . which in some places 

 passes into dolomite.' Cohen"* mentions its occurrence in the 

 Transvaal and in Griqualand West. Gibson does not appear to 

 have come across it, since he does not mention it. Molengraaff 

 calls it Malmani Dolomite/ from its occurrence at that locality. 

 Mr. Draper has also described this rock.^ 



Distribution in the Southern Transvaal. 



The Dolomite and its accompanying cherts bulk more largely 

 among the rocks of this district than perhaps any other formation. 

 The most northerly belt has its northern margin immediately south 

 of Pretoria, while its southern margin is in contact with the granite, 

 the junction being of course a faulted one. The dip is to the north, 

 the beds constituting the northern limb of an anticline, the southern 

 limb of which is found some 10 miles south of Johannesburg. The 

 two belts come together at Wonderfontein, 20 miles south-west of 

 Krugersdorp, the older beds disappearing entirely under the 

 dolomite arch. Twenty miles farther west they reappear, and 

 separate the Dolomite again into a northern belt with a south- 

 easterly dip and a southern with a north-westerly dip. The 

 southern belt can be followed to the Vaal Eiver, which it crosses a 

 few miles south-east of Klerksdorp. 



South-east of Johannesburg the southern dolomite-belt circles 

 round and, striking south-west, forms the valley of the Klip E,iver, 

 and finally passes under the Karoo Pormation at Yereeniging. A 

 narrow band of the Dolomite forms the outer ring of the southerly- 

 dipping beds round Yenterskroon. According to its dip, it would 

 appear to underlie the quartzites and conglomerates of the Wit- 

 watersrand Beds that occur here ; but its anomalous position is 

 due to reversed faulting. 



No recognizable fossils have yet been found in the Dolomite 

 Pormation, although Cohen '^ mentions the occurrence, near the 

 Makwassispruit, between Klerksdorp and Potchefstroom, of im- 

 pressions of crinoids and brachiopods resembling Orthis and Chonetes. 

 In places a well-developed oolitic structure is observable in the rock, 

 especially in the siliceous layers. 



^ Zeitschr. der Deutseh. geol. Gesellsch. vol. xli (1889) p. 578. 

 2 Quart. Journ. Geol. Soc. vol. xli (1885) p. 576. 

 ^ ' Geological Features of the Transvaal,' London, 1891, p. 6. 

 * Dahms, Neues Jahrb. Beilage-Bd. vii (1891) p. 117, and Gotz, ibid. Beilage- 

 Bd. iv (1886) p. 116. 

 ® Op. jam cit. p, 218. 



^ Quart. Journ. Geol. Soc. vol. 1 (1894) p. 561. 

 ' Dahms, op. jam cit. p. 118. 



