AND ASSOCIATED KOCKS OF TilE SOTJTHEKN' TRANSVAAL. 425 



Mynpacht Mine property (see fig. 8, p. 431), lying about 9 miles 

 S.S.E. of Boksburg, coal has been discovered, and is worked for the 

 use of the 'battery' and mine-engines. In a short visit which the 

 writer paid to the coal-shaft there were found lying on the surface 

 several pieces of dark limestone breaking with a conchoidal fracture 

 and resembling in appearance the 'peldon' bands and Spirorhis 

 limestone of the Upper Carboniferous measures of England. No 

 fossils were discovered in it. 



Wherever the writer has seen the coal-bearing beds of the Orange 

 Free State — near Klerksdorp, Kroonstad, and Wynburg — they are 

 identical with those of Boksburg and Heidelberg. In the river at 

 Kroonstad a very good section of the horizontal olive-white and 

 yellow sandstones is exposed. In the Heidelberg and Boksburg 

 districts the coal lies in detached basins.; these basins are very 

 shallow in the Transvaal, but in the Orange Free State the coal- 

 strata will probably be found to constitute much thicker deposits, 

 while it is certain that they cover much wider areas' than in the 

 neighbouring Eepublic. 



From the fact that the coals contain a large quantity of fine black 

 shaly material, and that underclays are invariably absent — coarse 

 sandstones forming both ' roof ' and ' floor,' — it is highly probable 

 that the coals are of drift and lacustrine origin. This conclusion is 

 also supported by the fact that all the evidence tends to point to 

 their Karoo or post-Karoo age. For, as it seems generally agreed 

 among all those who are personally acquainted with South African 

 geology that the present central plateau is of pre-Karoo age, the 

 Karoo and Stormberg beds must be of terrestrial and freshwater 

 origin. Now, in the Orange Free State the coal-beds are of acknow- 

 ledged Upper Karoo and Lower Stormberg age, and it seems certain 

 that the coals of the Transvaal and of the Orange Free State belong 

 to one and the same geological formation. 



A detailed account, however, of the coal-beds of the Transvaal is 

 beyond the scope of this paper. What is learnt from them in refer- 

 ence to the Keef Series is, that the interval between the tilting and 

 the denudation of the latter and the deposition of the coal-bearing 

 strata was a long one. Ultimately the Southern Transvaal seems to 

 have been converted into a lake-basin, or more probably into a series 

 of lake-basins, into which logs of timber and other drift-materials 

 were floated, their relics constituting the present coal-seams. 



3. The Faults^ Dyhes, and Igneous Rock-masses of the 

 Witwatersrandt. 



In a series of rocks which from constitution and alteration are so 

 similar that no distinctive band can be certainly settled to have a 

 definite horizon, and where the outcrops are largely concealed be- 

 neath superficial deposits, it is of course impossible to lay down the 

 position and direction of the faults with complete accuracy. The 

 directions of those inserted upon the accompanying Map (PI. XI.) 

 are thus more or less inferential, but it is believed that in no case 



