366 THE ZUURBERG VOLCANIC FISSURE 



Silver Dam and Saltpetre Kop pipes as well. We have 

 already seen that the Karroo dolerites are posterior to 

 the Stormberg vents and volcanics, therefore the period 

 of activity represented by the kimberlite and other pipes 

 is later still, e.g., not earlier than the Lower Jurassic. 

 If the resemblance of the Spiegel River melilite-basalt 

 to the similar rocks of Sutherland be considered as 

 evidence of their belonging to one and the same phase 

 of volcanic activity, as in our opinion it may be, then 

 the earlier limit of the pipes is advanced from Jurassic 

 to Neocomian or post-Neocomian times. 



It is worth while mentioning the fact that the other 

 known African rocks containing melilite and having a 

 distinct, though perhaps not very close, resemblance to 

 the Colonial melilite-basalts occur in East Africa at 

 Doenyo Ngai, Makinga Hill and Mount Elgon. 1 The 

 East African rocks, however, are of quite recent date. 



THE ZUURBERG VOLCANIC FISSURE. 3 



A fault with southern downthrow separates the Uiten- 

 hage beds from the older rocks to the north in the 

 Divisions of Alexandria and Uitenhage. The whole ex- 

 tent of this fault has not yet been examined, but from 

 the Mission Station at Enon for a distance of nineteen 

 miles eastwards a remarkable group of lavas, breccias and 

 tuffs occupies a position along the fault. This volcanic 



1 Short descriptions of these rocks are given in Zirkel, L&hrbtich der 

 Petrographie, 2nd edition, vol. iii., p. 25 ; Rosenbusch, Mikroskopische 

 Physiographic, etc., p. 1276. G. T. Prior has described the Mount Elgon 

 rocks in Min. Mag., 1903, p. 228. 



2 For more detail see T. S. A. P. S., vol. xvi., p. 189, and G. C., x., 

 pp. 34-42. 



