772 H. A. BROUWER 



Waterberg system ; they have here been entirely removed by denu- 

 dation. Humphrey mentions that there are no signs of the presence 

 of Waterberg rocks among the stratified lavas, nor were any frag- 

 ments of those rocks found among the volcanic breccias, while 

 many examples of included granite boulders within the Pilandsberg 

 rocks were found. 



He concludes that the volcanic outbursts and the outpouring 

 of lava postdated the removal of all of the sedimentaries of the 

 Waterberg system in this neighborhood. No evidence is available 

 about the age of the Pilandsberg rocks with regard to the Karroo 

 system. 



Of course, if the possibility of overhead stoping is admitted, the 

 problem of the age of the Pilandsberg rocks is more complicated, 

 but the question of the mechanism of intrusion is still too vague 

 for further discussion. 



OTHER OCCURRENCES OF NFPHELINE SYENITES AND ALLIED ROCKS 



The occurrence of nepheline syenites on Leeuwfontein [320] and 

 Zeekoegat [287] was discovered by Molengraaff in 1898. 1 The 

 numerous variations of the Leeuwfontein foyaites in chemical and 

 mineralogical composition and also the leucocratic and melano- 

 cratic dike rocks, bostonites, monchiquites, tinguaites, etc., were 

 described. Liebenerite porphyries, like those which occur at 

 Predazzo in the Tyrol and at Alno (Sweden), are also associated with 

 the nepheline syenites of this region. 



D. Draper discovered nepheline syenites on Walmansdal[n6] 

 to the northwest of Zeekoegat [287]. The rocks to which J. A. L. 

 Henderson 2 gave the name hatherlite were also collected on Leeuw- 

 fontein [320]. As was stated by Molengraaff, 3 the name hatherlite 

 is not applicable because the old powder factory "Eerste fabrieken" 

 or "Hatherley factory" is situated to the south of the Magaliesberg 

 Range and has nothing to do with the factory on Leeuwfontein [320]. 



1 G. A. F. Molengraaff, "Note on Our Present Knowledge of the Occurrence of 

 Nepheline Syenite in the Transvaal," Trans. Geol. Soc. South Africa, VI (1903), p. 89. 



2 J. A. L. Henderson, On Certain Transvaal Norites, Gabbros, and Pyroxenites and 

 Other South-African Rocks, London, 1898. 



3 G. A. F. Molengraaff, Geology of the Transvaal (Johannesburg, 1904), p. 46. 





