478 Annals of tJie Sontli African Museum. 



but the bulk of the stud' is of sedimentary origin, and in places it 

 passes into a pale yellowish-green sandy rock with few foreign 

 fragments, some of this passing by degrees into Cave Sandstone. 

 Fragments of Cave Sandstone and red and purple shales and sand- 

 stone are present, blocks of basalt up to 6 feet across and lumps of 

 Molteno grit as much as 7 ft. in length. 



The history of the pipe must have been somewhat as follows: - 

 At the close of the period of deposition of the Red Beds a small 

 volcano came into action on this spot and gradually enlarged its 

 boundaries, portions of the margin (composed of Red Beds) slipping 

 down at intervals into the vent. Then the Cave Sandstone com- 

 menced to be formed and was deposited at an angle over the denuded 

 hollow encircling the agglomerate neck. Sediment would become 

 mingled with the fragmental material within the pipe, while occasional 

 volcanic explosions would account for the ashy streaks and patches 

 in the Cave Sandstone at several points close to and outside the 

 pipe. On the south-west margin the fragmental matter most probably 

 represents an indipping patch of stratified ash overlying the sandstone". 



This occurrence is by no means an isolated one; and the matter 

 will be furthered discussed later in the section. 



The other difficulties which stood in the way of Professor Schwarz's 

 acceptance of the Cave Sandstone as a product of ordinary denu- 

 dation seem to disappear if we consider that the climate underwent 

 a further approach to aridity, and that from the onset of Molteno 

 times there was a gradual secular climatic change in one direction 

 throughout the formation of the deposits of the Stormberg Series. 



We have seen that the base of the Cave Sandstone is generally 

 red and often bedded - this indicating a continuance of the Hood- 

 plain deposits of the semi-arid Red Beds time. The massive portion 

 of the Cave Sandstone has, however, as du Toit (1918) has pointed 

 out, practically all the features of an aeolian deposit such as the 

 Pleistocene loess of the Northern Hemisphere. 



In its typical form the loess of Asia and Europe is a line-grained 

 deposit, consisting of minute particles of hydrated silicate of alumina, 

 quartz, felspar, mica, and other minerals, more or less cemented by 

 calcium carbonate, the segregation of which gives rise to concretions. 

 It is also often impregnated with alkaline salts, and nearly always 

 stained yellow with ferruginous matter. Its homogeneity of compo- 

 sition and structure contrasts it with all water-deposits. There is an 

 almost complete absence of any stratification, and the particles of 

 mica in it are uniformly distributed without orientation. A charac- 

 teristic feature is its well-marked vertical jointing. Its fossils consist 



