746 H. A. BROUWER 



Bushveld complex, the volcanic series, and the sandstone series, of 

 which the contradictory facts already were enumerated by Molen- 

 graaff, 1 has not been solved in this way. 



As far as concerns this mutual relation, the following facts can 

 be considered as certain: 



i. The deep-seated rocks are intrusive in the volcanic series. 



2. Dikes which are genetically connected with the deep-seated 

 rocks (felsophyres with the red granites, tinguaites with the 

 nepheline syenites) cut through the sandstone series. 



3. The volcanic series show the characteristics of effusive rocks 

 and include sediments (shales and sandstones) in the higher 

 horizons. 



4. Sometimes more, sometimes less, clearly the sandstone series 

 rest unconformably upon the volcanic series, the transition being 

 characterized by the existence of conglomerates. 



5. In the basal conglomerate of the sandstone series felsitic 

 pebbles sometimes occur. 



6. Fragments of a conglomerate, which very closely resembles 

 the basal one, are found in the phonolites of the Pienaars River 

 valley. 



When we try to make these facts agree with each other, we meet 

 with great difficulties. It seems to be certain that an effusive 

 period has preceded the main intrusion and that both are connected 

 genetically. 



But when we admit, for instance, that the sandstone series are 

 older than the effusive and intrusive series, then the occurrence 

 of felsitic pebbles in the basal conglomerate and the more or less 

 distinct unconformity with regard to the felsites, and also the effu- 

 sive character of the latter ones and their alternation with sedi- 

 ments, are inexplicable. When we admit that the sandstone series 

 are younger than the effusive and intrusive period, then the inter- 

 secting dikes, which are the equivalents of the deep-seated rocks, 

 and also the intrusions of red granite in the sandstone series are 

 unexplained. 



We could explain the facts in a rather satisfactory way if we 

 admitted effusion and several intrusions from a deeper-seated 



1 G. A. F. Molengraaff, Geology of the Transvaal (Johannesburg, 1904), p. 59. 



