470 Annals of the South African Museum. 



shows nearly similar features, but microcline felspar is present in 

 addition and the rock contains somewhat more mica". 



Two main views have been put forward as to the mode of origin 

 of the Cave Sandstone. We will consider first that of Professor Schwarz 

 as developed in a paper in the Trans. S. Afr. Phil. Soc. Vol. XVI 

 (1905) p. 30. 



Schwarz considers that the Cave Sandstone is a tuff, blown out of 

 the volcanic vents which opened the period of Drakensberg volcanic 

 activity, a portion of which still, in some cases, remains in the throats 

 of the vents. "If" he says "the Cave Sandstone was formed before 

 the production of the material in the pipe, then the latter ought to 

 be made up of portions of all the rocks which the vent traverses, 

 but we find that this is not the case, and that the material in the 

 pipe is identical with that of the Cave Sandstone. The Cave Sand- 

 stone, however, contains 83-5 / of Si0 2 , with grains of quartz, 

 microcline, plagioclase, zircon, rutile, tourmaline, chlorite, garnet and 

 epidote, while the lavas of the Drakensberg - - some of which flowed 

 out of the pipes - - are basic in composition". Therefore, says Schwarz 

 in effect, the pipes must have tapped deep-seated rocks such as the 

 granites and crystalline schists -- outcrops of which occur in Natal - 

 and the triturated material from them forms the Cave Sandstone. 

 The author of this theory does not believe that the Cave Sandstone 

 was formed by ordinary denudation from land-surfaces, as no land 

 surface of a requisite nature was near enough at hand. He agrees 

 that the Molteno Beds are the detritus of a granitic region, presum- 

 ably of the southern prolongation of the Madagascar ridge ; but argues 

 that the break in the deposition of the Molteno Beds marked the 

 disappearance of the source of the supply. In conclusion he states 

 "In the Cave Sandstone we have many peculiar features that could 

 be explained by the supposition that it flowed from the crater mouths 

 as a. mud. It is hard otherwise to account for the immense thickness 

 of the embedded mass; it is hard to explain the sudden change of 

 great thicknesses of the white rock to a red clayey material; and 

 still more mysterious is the pseudo-bedding that one can see at 

 N'quatsha's Nek, where the stratification is just such as would be 

 produced had the whole been stirred round in a gigantic pot like a 

 pudding". 



The same author, in his "Causal Geology" (1910) speaks of the 

 Cave Sandstone as a "non-volcanic tuff' ; and in "South African 

 Geology" (1912) says the Cave Sandstone" consists of rounded grains 

 of quartz and felspar which have been corroded on the surface and 

 enveloped with minute scales of talc ; thus the ordinary aspect of a 



