776 H. A. BROUWER 



also often limited to the aegirine foyaites and the arfvedsonite 

 foyaites and are wanting in the foyaites with barkevikitic amphi- 

 bole. The rare minerals and a not very small quantity of lime in 

 the magma seem to exclude one another (compare the analysis of 

 the normal foyaite of Leeuwfontein, which has been given in my 

 previous paper) . The association of foyaites with leeu wf onteinites 

 which besides barkevikite also contain plagioclase makes it 

 probable that the CaO content of the common mother-magma was 

 rather considerable. 



The rocks of the neighborhood of Leeuwfontein [320], which 

 hitherto have been studied under the microscope, belong to the 

 following groups : 



1. Aegirine foyaites 

 Leucocratic rocks 

 Pienaarites (melanocratic rocks 

 rich in titanite) 



2. Aegirine-amphibole foyaites 



3. Tawites 



4. Feldspar rocks 



5. Aegirine-foyaite porphyries 



6. Aegirine-amphibole foyaite por- 

 phyries 



7. Leeuwf onteinites 



8. Leeuwf onteinite porphyry and 

 monzonite porphyry 



9. Tinguaite porphyries 



10. Monchiquites 



11. Augitites 



12. Andesitic camptonites 



13. Doleritic nepheline basalts 



14. Diabases 



15. Liebenerite porphyries 



16. Bostonites 



17. Phonolites 



H. Kynaston 1 mentions that the foyaite of Walmansdal [116] is 

 clearly intrusive in the "felsites." 



Nepheline syenite region to the west of Lydenburg. 2 — This region 

 covers a surface which has about the same extension as that on 

 Leeuwfontein [320]. It is surrounded by red granites and occurs 



1 H. Kynaston, "The Geology of the Country Surrounding Pretoria," Explanation 

 Sheet I, Geol. Surv. of the Transvaal, 1907, p. 28. 



2 A. L. Hall, in Annual Report Geol. Surv. of the Transvaal, 1910. 



