Fauna and Stratigraphy of the Stortnberg Series. 477 



sandstone is entirely masked and the rock has the appearance of chalk. 

 The sandstone is not an ordinary sediment for the fine coating of talc 

 scales would have been soon rubbed olY the sand grains if they had 

 been dragged along the sea floor by currents, and the coating could 

 not have formed after the sandstone was consolidated .... The non- 

 volcanic material torn from the granite walls of the chimneys would 

 issue as fine sand, and the corrosive action of the hot gases in the 

 vent would account for the alteration of the grains on their surfaces". 

 The features shown bv the Cave Sandstone, when considered with 



^ 



the other members of the Stormberg Series, do not seem to call for 

 any such mode of origin as is outlined here. It seems that the 

 presence, of Cave Sandstone infilling some of the pipes led mainly to 

 the formation of the theory. Du Toit has studied a peculiar pipe 

 of this nature and has published the following description. 



JHUL TtR Iff. S T/J T1ON 

 8323 



Fig. 55. Diagrammatic section through Volcanic Neck of Thule after du Toit. 



Length about 4 miles. 



"A very interesting occurrence in view of the information which 

 it yields upon the conditions of deposition of the Cave Sandstone, 

 is the large volcanic neck on the farm Thule (Griqualand East ). 

 almost on the crest of the Drakensbergen. It is nearly a mile across 

 with somewhat irregular outline, and occupies a hollow hemmed in 

 by Cave Sandstone, while several narrow ravines have trenched the 

 area and laid bare good sections. The peculiar feature in this neck 

 is that the Molteno Beds and Red Beds are lying quite undisturbed 

 right to the very edge of the pipe, but the Cave Sandstone, on the 

 other hand, commences to show an inward dip at a distance from 

 the margin of the latter, varying from about a quarter of a mile 

 on its eastern side to well over a mile on its west side. The sheet 

 of sandstone curves downward over the denuded edges of the Red 

 Beds, and in places possesses dips of as much as -4CT, passing below 

 dark greenish agglomerate at the extreme south-west end, but 

 appearing to abut against the volcanic infilling at other points. 



The material within the pipe consists of medium-grained agglo- 

 merate with fragments of basalt and amygdaloid of various kinds, 



