56 Transactions of the South African Philosophical Society. 



The unequal weathering of the sandstone often gives rise to large 

 caves, some capable of sheltering several thousand sheep, and hence 

 the name first given to the formation by E. J. Dunn. In many of 

 the caves there are still drawings and paintings done by the Bush- 

 men who formerly inhabited this area, and whose crude weapons 

 and implements are occasionally picked up. The Cave sandstone 

 is usually remarkably uniform in character throughout this area, but 

 in parts of Wodehouse and Barkly East the central portion of the 

 bed is pale bluish in colour and very fine grained, passing almost 

 into a mudstone. 



Under the microscope the sandstone is seen to consist of abundant 

 angular to sub-angular grains of quartz, fairly uniform in size, set 

 in a pale, almost colourless, ground mass. There are also fragments 

 of orthoclase, plagioclase, and microcline felspar, flakes of white 

 mica, and grains of zircon, epidote, and tourmaline in small quantity. 



It has been suggested that the Cave sandstone is, in part, of vol- 

 canic origin, containing much finely-disintegrated material ejected 

 by the volcanoes, and derived from granitic and metamorphic rocks 

 deep down below the surface of the earth. 



Against such a view I must, however, protest, for there seems 

 to be no evidence to support it. Everything, in fact, points to the 

 Cave sandstone being a normal type of sediment. 



The thickness of the Cave sandstone is variable. The maximum 

 yet known in the Colony is 800 feet, occurring at the Barkly Pass ; 

 but in Natal Mr. Churchill records a similar value. This makes it, 

 I believe, the thickest unbedded stratum of sandstone known to 

 geologists. 



More commonly it varies from 200 feet to 400 feet, but in a 

 number of places the sandstone is either very thin or entirely un- 

 represented, the Volcanic rocks resting directly upon the Eed beds. 



Fossils occur but sparingly in the Cave sandstone, and are 

 chiefly reptilian in character. The age of the Eed beds and Cave 

 sandstone is probably the same as the Lias (Lower Jurassic) of 

 Europe. 



Having now placed on record the characters of the sedimentary 

 rocks of the Stormberg series, we have next to consider the source 

 of the sediments which go to form them and the conditions under 

 which the materials were deposited. 



III. — Physical Conditions during Sedimentation. 



It is well known that all the sedimentary rocks of the Karroo system 

 were laid down in a large lake or inland sea whose boundaries are as 

 yet known only approximately. 



