ALKALI ROCKS IN THE TRANSVAAL 763 



plex is again largely developed. It covered the whole region, 

 which is limited to the south by the Schurvebergen and Zeerust 

 Hills, to the west by the Marico Hills, and to the north by the 

 Dwarsbergen. 1 



In following the basic margin along the western boundary of 

 the Pilandsberg, we find quartzites in the northern part of Vogel- 

 struisnek [602] which are in immediate contact with red syenites. 

 More to the north the latter rocks border again upon norites. 

 Near, and west of, the native stadt on Ruigehoek [426] norites rich 

 in feldspars are exposed in the valley of a rivulet ; they are the same 

 rocks as those which are found to the south of the Pilandsberg, but 

 show a pronounced schistose structure and a dip to the northeast. 

 To the west the rocks become more basic, and near the contact 

 with the quartzites on Davidskuil [142] very basic rocks were 

 collected in the valley of a rivulet which is crossed by the road from 

 the native stadt on Mabieskraal [620] to Janskop on Bierkraal [545]. 

 They, too, show a pronounced schistose structure. Here the strike 

 is about N. 15 W., and the dip is to the east-northeast. 



. On Tusschenkomst [446], to the east of the quartzite hill Janskop 

 on Bierkraal [545], a series of hills consisting of schistose basic 

 rocks can be followed in a north-northwesterly direction. Hum- 

 phrey 2 mentions a peculiar feature of the pyroxenites, particularly 

 noticeable on the farms Ruigehoek [426] and Zandspruit [181], 

 where narrow bands of chromite, dipping to the east, have formed a 

 band of comparatively high ground and an apparent stratification. 



From all that has been said above, it is evident that the basic 

 margin of the plutonic complex is cut of abruptly by the intrusion 

 of the Pilandsberg. 



Granites : The red granites of the igneous complex of the Bush- 

 veld are found to the east of the norites. The boundary between 

 the two rock types crosses the Elands River in the southeastern 

 part of Rhenosterfontein [867] and ends against the alkali syenites. 

 The red granites are found all along the eastern part of the 

 Pilandsberg; on Saulspoort [269], west of the Rustenburg road, the 



1 F. H. Hatch, Trans. Geol. Soc. South Africa, VII (1904), p. 1. 



2 "The Geology of the Pilandsberg," Annual Report of the Geol. Survey of South 

 Africa, 191 1, p. 81: 



