36 Transactions of the South African Philosophical Society. 



crushing is to produce irregular masses of pulverised rock, heated 

 more or less highly, that may extend to any depth within the earth's 

 crust ; but it is only to such depths as water can percolate that the 

 deepest focus of volcanic activity can be found.''* In the Drakens- 

 berg the volcanoes are situated on a line of crustal deformation.! A 

 large number of the vents have brought only solid rocks to the 

 surface, fragment and boulders of granite and crystalline schists— 

 though I had only to record the presence of a single fragment of 

 crystalline limestone among the boulders in Matatiele, yet the tuffs are 

 sufficiently good evidence to ground my argument upon with this 

 isolated boulder, for I unfortunately had a very limited time in which 

 to prosecute my investigations, and was hindered by the regulations 

 consequent on the war that was then raging while I was surveying 

 the Matatiele Division, and, also, I was working in an altogether 

 new area. It is very improbable that a single boulder of the older 

 series should exist in the whole district. 



Bound Molteno there are a number of vents, of which Telemachus 

 Kop is the largest ; Mr. Dunn says that among the rocks in the neck 

 there are many that are quite unlike any in the district. Mr. du 

 Toit, also, in Elliot J found bluish white quartzites that are probably 

 derived from the Table Mountain series or perhaps from the Dwyka 

 conglomerate lying between the Table Mountain sandstone and the 

 newer sedimentaries. In Sutherland Mr. Bogers definitely records 

 Table Mountain sandstone in the pipes in the Saltpetre Kop area 

 along with granites, mica-schist, grits, and shales, so that the rock 

 did undoubtedly come from the underlying basement of the Karroo 

 sedimentaries. § 



The simple fact of having these solid rocks brought up in the 

 volcanic pipes, proves to my mind that the chimneys cannot have 

 their origin in really profound depths in the earth's crust, for had 

 they so penetrated, the enormous pressure that exists at such depths 

 would have brought the molten rock welling to the surface to the 

 exclusion of all solid material. We seem, therefore, in the Drakens- 

 berg to get what was wanting in the Baviaan's Kloof folded area, 

 namely, an enormous force applied to a rock-mass containing a flux, 

 and sufficiently deep in the earth's crust to keep the fracturing of 

 the rock under, and thus to concentrate the effects of the force. As 

 the mass acted upon contained limestone, as witness again the lime- 



* Phil. Trans., vol. clxiii. p. 167. 



f Volcanoes of Giiqualand East, Trans. Phil. Soc, Cape Town, 1903, vol. xiv. 

 p. 98; Ann. Hep. Geol. Comm., 1902, Cape Town, 1903, p. 39. 

 J Ann. Hep. Geol. Comm., 1903, Cape Town, 1904, p. 193. 

 § Ibid., pp. 61-63. 



