AND ASSOCIATED fiOCKS OF THE SOUTHERIf TRANSVAAL. 429 



(2) This series is certainly much neiuer than the locally eroded 



schists, granites, and gneisses which now underlie it. On 

 the other hand, the gold-bearing conglomerates and associated 

 rocks are very much older than the horizontal coal-bearing 

 beds which overlie them unconformably. 



(3) The occurrence of pebbles of red sandstone in some of the reefs 



shows that there must have been a still older series of sand- 

 stones from which these pebbles were derived. This older 

 sandstone series may yet be discovered. 



(4) The entire series of beds associated with the gold-bearing con- 



glomerates has been (at least locally) thrust over the gneisses 

 and schists, and was not originally deposited in its present 

 position, 

 (o) The movements to which the beds have been subjected have 

 taken place in two directions — the more intense movement 

 being from south to north, and a less effective one from east to 

 west. The result of these two movements is that the beds now 

 occupy a basin-shaped area, along the margins of which the 

 strata have everywhere given way ; while the rocks have been 

 crushed, overthrust, and altered locally into schists, quartzites, 

 pseudo-quartzites, and gneisses. 



(6) After the cessation of these earth-movements the strata were 

 injected with igneous material of basic and sub-basic types ; 

 and much of the country was flooded with lavas of the same 

 character. The presence of the iron pyrites, so abundant in 

 the quartzites and conglomerates, has probably some con- 

 nexion with this volcanic outburst. 



(7) The conglomerates seem to have been formed mainly at the ex- 



pense of the underlying granites and schists, which may have 

 contained numerous veins and larger masses of auriferous 

 quartz. 



(8) Some of the newer schist in the conglomerate-bands seems cer- 



tainly due to metamorphism arising from pressure and move- 

 ment acting since the conglomerates were deposited. 



III. GEOLOGY OF DISTRICTS OUTSIDE THE TYPICAL 

 WITWATERSEANDT AREA. 



1. The Chimes Mine and Heidelberg Districts. 



As the rocks of the typical area have been described somewhat 

 fully, the strata of similar age met with in other parts of the 

 Transvaal wiU be treated of in a more cursory manner, sufficient 

 details only being given to throw light upon the general structure of 

 the country. 



Although the geology of these outlying districts looks at first 

 sight far more complex than that of the Johannesburg area, their 

 structure is really much simpler. It soon becomes evident on exa- 

 mination that the strata have been thrown generally into shallow 



Q.J.G.S. No. 191. 2h 



