The Volcanic Fissure under Zuurberg. 195 



steep face of Witteberg quartzites dipping at angles of 70°-80° 

 S. 15° W. It ends below in bush-covered slopes, but along the 

 cattle track from Mimosa to Nieuw Post there are several outcrops 

 on the divide between the steep kloofs descending east and west. 

 The northernmost 700 yards or so of the divide is sandy ground 

 sprinkled with quartzite fragments and overgrown with bush. If 

 the Dwyka conglomerate occurred here I think it would show itself, 

 at least in fragments, as it does so in similar situations further 

 west ; the Lower shales do not make themselves so prominent, and 

 they may or may not be present. South of the sandy ground one 

 first meets with a brown micaceous sandy rock with bright green 

 spots, a rock quite different from any known from the Dwyka series, 

 and it certainly belongs to the very varied tuffs of the neck ; then 

 follow soft and quartzitic breccias with many fragments of Witteberg 

 or other quartzite, then comes a peculiarly bright green breccia with 

 fragments of sedimentary rocks in it, and this is followed by a soft 

 pink tuff, which soon gives place to a red tuff with vesicles partly 

 filled up, and this again to a soft red or white mottled tuff, which is 

 followed by buff-coloured breccias with much quartzite in them ; 

 soft pink tuff is the last, and southernmost, fragmental rock of this 

 neck. About 20 feet from the last outcrop of tuff the usual amygda- 

 loidal lava is met with, but it contains a great quantity of tuff caught 

 up when it was in a fluid condition. 



A good number of outcrops of the lava were found by following 

 the ridge along which the track goes to Mimosa, but there was no 

 tuff seen on this ridge. The lava varies in compactness by the 

 increase or decrease of the amygdales. The amygdales are of 

 various minerals; calcite and chalcedony occur, but zeolites are 

 more common. It was curious to find large chalcedony amygdales 

 that look as if they might have come from the Vaal Eiver. 



In a garden at the end of this lava ridge in the main valley on 

 Mimosa there is a larger outcrop of the lava than is usually met 

 with, and in it are seen bands of more and less vesicular lava, with- 

 out any definite dividing plane. There are also irregular bands of 

 pipe amygdales ; these are arranged perpendicularly to the layers of 

 varying texture, and individually may reach a length of 3 inches. 

 All these layers dip towards S. 10° W. at an angle of 20°. The 

 occurrence of the pipe amygdales, which were noticed again on the 

 Duncairn boundary though not in place, is very remarkable, for they 

 have hitherto been found only in surface lava flows. 



Going up the valley north of this garden one does not find out- 

 crops till one passes a well sunk in the Dwyka conglomerate, above 

 this only the Dwyka and Witteberg series are seen. 



