198 Transactions of the South African Philosophical Society. 



Matatiele runs more or less parallel with the Pondoland coast and 

 the post-cretaceous faults on that coast. 



In East Africa the recent volcanic rocks are connected with the 

 downthrown areas called the Eift Valleys, but they present no precise 

 parallel with the Zuurberg volcanic belt. 



There can be no doubt that the eruptions along the Zuurberg fault 

 took place after the deposition of the Uitenhage beds, which are of 

 Lower Cretaceous age, but the only later limit which can at present 

 be set to the event is laid down by the fact that the tops of the vol- 

 canic ridges are cut down to a surface which was once continuous 

 with the Zuurberg slope ; and these tops are still capped in places 

 by gravel similar to that on the main slope, from which they are now 

 separated by valleys several hundred feet deep. No trace of lava 

 flows or beds of ash ejected from the fissure has been found on 

 Zuurberg or the country to the south. If such materials were ever 

 thrown out they have long since been swept away. Although there 

 is no direct evidence of surface outflows, the highly vesicular 

 character of the lava shows that there must have been open access 

 to the air, otherwise the water vapour could not have expanded so 

 freely. The total absence of recognisable lava fragments in the 

 breccias and the relationship of the tuffs and lava show that the 

 violent explosions which produced these breccias were succeeded by 

 the more gentle rise of the lava. The explosions occurred not only 

 at the well-defined enlargements of the fissure but at so many other 

 places, as shown by the presence of breccia and tuff at intervals 

 throughout, that we may regard the whole line as having once been 

 their site, but the direct evidence of this is now lacking owing to 

 the rise of the lava and its replacement of the fragmental rock. 



As to the origin of the material forming the tuffs and breccias 

 little can yet be said, but quartzites like those of the Witteberg 

 series are the most abundant recognisable rocks in them. 



