106 Transactions of the South African Philosophical Society. 



■of the older lavas which had Ijeen produced by erosion during a 

 period of rest from volcanic activity. Here also three thin dykes of 

 dolerite cross each other at a particular point, and they can.be 

 traced for many miles running each in a straight direction through 

 the horizontal beds of amygdaloid. 



Between George Moshesh's country and Makomereng there is a 

 larger dyke of dolerite which thickens out to an enormous mass in 

 Maklagala's country and thins out gradually on either side. The 

 •direction of the great dyke is not quite parallel to the present line of 

 the Drakensberg crest, but approximates more nearly to the general 

 direction of the line of volcanoes. Sections showing the relationship 

 of the dolerite to the amygdaloid are not frequent, but on Mako- 

 mereng there are some which show the dolerite cutting through the 

 lower beds of lava, and then bending over and covering these as a 

 thin sheet, which again is covered with more amygdaloids. 



I was not able to determine finally whether the dolerite was only 

 intrusive between the amygdaloids or had been poured out on the 

 surface and then covered with more vesicular lavas. I am strongly 

 inclined to believe that the latter was the case, both from the 

 appearance of the rocks in section, and also since the dyke in some 

 places is curiously mixed up with the encasing wall, and appears to 

 have arisen explosively in the crack ; in another place the amygda- 

 loidal lavas seem to be in continuity with the dolerite of the fissure. 

 It is very doubtful, also, Avhether such an immense iDody of molten 

 rock could come so near the surface as this one did without pouring 

 out some of its material. It is an interesting point which I hope the 

 petrographical examination of the rocks will be able to clear up, for 

 if it proves to be a true fissure of eruption we have a splendid 

 ■example of a phenomenon which has been surmised to exist from 

 theoretical considerations, but never yet actually found to exist. 



South of this there is a smaller dyke which has also the appear- 

 iince of having arisen explosively in its crack, for it includes many 

 fragments of the wall of the dyke included in the substance ; the 

 igneous rock and the north wall is intensely crumpled and injected 

 with small dykes, and these phenomena are unknown in the ordinary 

 dykes of the district. Further west again, near Rankakata's Nek, 

 there is another great dyke with the lava apparently pouring over 

 the surface of the sandstone, but the surface features have been too 

 much eroded to allow of any definite statement to be made as to the 

 nature of the fissure. 



Before going into the consideration of these volcanoes in regard 

 to their tectonic aspect, I should like to mention the Cave Sandstone 

 which lias puzzled me exceedingly. It is a soft granular sandstone, 



