562 ME. D. DKAPEE ON THE OCCURRENCE OP [N"oV. 1894, 



course of the Mooi Eiver. In the calcareous quartzite before alluded 

 to the river has, in course of time, worn for itself a subterranean 

 course by dissolving out, in the first instance, the little veins of 

 calcite, and then, when increasing volume gave it greater strength, 

 the quartzite also, the lime being again deposited as stalactitic 



formations in the caves Some parts of these quartzite beds 



are sufficiently calcareous to produce on calcination a valuable 

 lime." 



From these extracts from their writings it will be seen that both 

 Mr. Penning and Mr. Alford have described this rock from the 

 peculiarities that they have noticed where they examined it in situ. 

 Mr. Penning named it ' chalcedolite, in consequence of the chalce- 

 donic character frequently displayed.' Mr. Alford calls it a ' cal- 

 careous quartzite,' passing into dolomite, and superficially ' altered 

 into a species of chert.' 



Having had especial opportunities of examining this rock, especially 

 several deep workings in it in the Malmani district, I have come to 

 the conclusion : — 



lstly. That the ' elephant-rock ' occurring in various parts of the 

 Transvaal, but principally in the Potchefstroom, Lichtenburg, Mal- 

 mani, and Lydenburg districts, is really a dolomite, with thin 

 interstratified siliceous bands, for the following reasons : — 



(a) Its composition is 



48 per cent, carbonate of lime, 

 48 per cent, carbonate of magnesia, 

 4 per cent, silica. 



(b) That the residue, after the limestone has been removed by 

 the atmosphere, is a dirty-brown, soft, earthy matter similar 

 to manganese oxide. This occurs in all the caves, and in 

 between the siliceous layers, where it has heen long exposed 

 to the weather. 



(c) That the bulk of the rock is of the composition previously 

 mentioned (a), the bands of siliceous material being not 

 more than 10 or 15 per cent, of the whole mass where it has 

 not suffered from atmospheric influences. That the ' debris ' 

 from the rock consists largely of fragments of the siliceous 

 bands, strewn about on the surface, I admit ; but this only 

 occurs on the surface, and is tbe result of a large amount of 

 the calcareous portion of the rock having been removed. 



I submit that the alteration of a ' calcareous quartzite 

 into a ' dolomite,' and this again into a ' species of chert,' is, 

 to say the least of it, unique. 



2ndly. That this rock is intcrstratified between the Table-mountain 

 series (in which the conglomerate- beds of the Transvaal are situated) 

 and the quartzites of the Gats Rand (the ' quartzites of the 

 Zuurberg' of Bain) ; and in proof of this assertion I submit a section 

 (PI. XXIII.) taken by Dr. G. A. F. Molengraaf, Professor of Geology 

 in the University of Amsterdam, and myself, from Hartebeest-Fontein 



