ALKALI ROCKS IN THE TRANSVAAL 751 



fissures were formed, in which different minerals crystallized from 

 the circulating emanations of the magma. The numerous occur- 

 rences of tin ore are genetically connected with the red granites 

 of the Bushveld. The copper and silver ores of the Albert mine and 

 the cobalt ores of Balmoral are found in red granite. Finally, we 

 find numerous ore deposits in the Pretoria series, the origin of which 

 is probably directly connected with the intrusion of the Bushveld 

 complex. 1 



THE OCCURRENCES OF ALKALI ROCKS 



Common to the occurrences of alkali rocks is the abundance of 

 nepheline syenites. They are exposed at the following places: 



1. In the Pilandsberg (Rustenburg district), where they are 

 accompanied by syenites, effusive rocks, and dike rocks. 



2. At the boundary of the farms Leeuwfontein [320] and 

 Zeekoegat [287], northeast of Pretoria, where they are accompanied 

 by syenites, leeuwfonteinites, effusive rocks, and dike rocks. 



3. On the farms Rietfontein [451] and Spitskop [463], west of 

 Lijdenburg. 



4. On the farm Franspoort [426], south of Leeuwfontein [320] 

 (Pretoria district). 



5. On the farm Walmansdal [116], northwest of Leeuwfontein 



6. On the farm Leeuwkraal [396], still farther to the northwest. 



7. On the farm Losperfontein [119] (Rustenburg district). 



8. Numerous dikes can be followed from the Pilandsberg in a 

 northwesterly and a southerly to southeasterly direction. 



1 G. A. F. Molengraaff, Geology of the Transvaal (1904), p. 52; A. L. Hall, "Geo- 

 logical Notes on the Bushveld Tin Fields, etc.," Trans. Geol. Soc. South Africa, VII 

 (1905), 47-55; F. H. Hatch and G. S. Corstorphine, Geology of South Africa (London, 

 1909), p. 216; E. T. Mellor, "Field Relations of the Transvaal Cobalt Lodes," Trans. 

 Geol. Soc. South Africa, X (1907), 36; H. Kynaston, "Anniversary Address of the 

 President of the Geological Society of South Africa for 1908," Trans. Geol. Soc. South 

 Africa, XII (1909); H. Recknagel, "On Some Mineral Deposits in the Rooiberg 

 District," Trans. Geol. Soc. South Africa, XI (1908), 83; "On the Origin of the South- 

 African Tin Deposits," Trans. Geol. Soc. South Africa, XII (1909), 168; H. Merensky, 

 "The Rocks Belonging to the Area of the Bushveld Granite Complex in Which Tin 

 May Be Expected, etc.," Trans. Geol. Soc. South Africa, XI (1908), 25; H. Kynaston 

 and E. T. Mellor, "The Geology of the Waterberg Tin Fields," Memoir No. 4, Geologi- 

 cal Survey of the Transvaal, Pretoria, 1909. 



