196 Transactions of the South African Philosophical Society. 



At the place where two kloofs join to form the main valley a few 

 hundred yards east of the well, there is a small mass of buff and 

 pink tuffs, followed to the south by lava with many tuff inclusions. 

 This body of tuff seems to be a neck similar to, but smaller than, 

 the large neck below the Nieuw Post escarpment. 



A striking feature in the breccias is the absence of fragments of 

 the Dwyka conglomerate, but this may be due to lack of observa- 

 tions. The breccias and tuffs are different from any that have been 

 described from South Africa, but some of them show points of 

 resemblance to tuffs of the Stormberg area, and others are not 

 unlike some of the Saltpetre Kop breccias, so far as one can judge 

 from hand specimens. 



From this small neck I followed the lava up to the divide between 

 Mimosa (Thornleigh) and Duncairn along a bush-covered slope and 

 in the valley below ; there were very few outcrops, but the Dwyka 

 conglomerate was seen at one point in the stream bed, and nothing 

 but pieces of lava and tuff or breccia above this outcrop. On the 

 divide there is a short interval of covered ground between the Witte- 

 berg slope and the northernmost outcrop of lava ; there is no room 

 for the occurrence of the Dwyka conglomerate here, and probably 

 the Lower shales are also cut out ; south of the lava there is an area 

 500 yards wide on which tuff and breccias only occur ; these 

 resemble in general characters those on the large neck on the Nieuw 

 Post track, but they include a coarse breccia of the type seen in the 

 Coerney Eiver bed. The red tuff in the south part of the neck is 

 penetrated by lava, and numerous fragments of tuff occur in that 

 rock, which occupies a belt of country some 500-700 yards wide 

 south of the neck. To the east the amygdaloidal lava continues as 

 a band of about 600 yards wide for another mile. There is much 

 tuff mixed with the lava in places along this part of its course, and 

 at one spot a borehole was put down 250 feet through a rock 

 described to me as " pale-coloured sandstone," but of which I could 

 not see a specimen. It was probably a tuff like the buff or pink 

 tuffs of the larger necks. The lava is in contact with the Witteberg 

 quartzites to the north along this part of its course, and where the 

 lava ends the Enon conglomerate is in contact with the quartzites 

 without the intervention of the Dwyka series. It is interesting to 

 note that the front face of Witteberg quartzite on Duncairn is 

 shattered into a breccia, in precisely the same manner as along the 

 faulted contact with the Enon seen near the Waggwa road. The 

 angular pieces of quartzite are embedded in a matrix of still further 

 comminuted quartzite. There has been little addition of cementing 

 substance, and the breccia is now as a whole a much more fragile 



