482 Annals of the South African Museum. 



Sandstone is evidenced by many examples, especially in the south 

 of the region and towards the top of the formation. In Maclear 

 two beds of sandstone are intercalated in the lavas. It is interest- 

 ing, too, to note that the ash here contains fragments of Molteno 

 Sandstone up to 5 feet across, and a few blocks of pre-Karroo quart- 

 zite. These have evidently been torn oil' from below and thrown 

 out by volcanoes in the neighbourhood. 



Further north, in Barkly East and the neighbouring districts, in 

 a few places the Cave Sandstone is entirely absent, the volcanic 

 flows resting directly on the Red Beds. In the Barkly East Division 

 the formation is split up by numerous beds of lava and ash, both of 

 which are sharply defined from the sandstone. At Siberia in Wode- 

 hoiise, three bands of sandstone are intercalated in the lavas. At 

 the head of Bamboes Spruit in Herschel there are four such bands. 

 Near the large Belmore volcano in Barkly East the Cave Sandstone 

 contains numerous masses of vesicular lava up to four feet across, 

 the lower surfaces of which consist of pipe amygdaloid. Du Toit 

 has described a section near Barkly East Township showing pinkish 

 sandstone resting on a bed of ash and abutting at one end against 

 a sheet of doleritic lava; in the sandstone are embedded rounded 

 masses of altered doleritic lava. At Waterfall in the Barkly Division 

 there is a section showing alternation of volcanic and sedimentary 

 material, both the sandstones and the lavas having a lenticular 

 character; there are pipe-amygdaloids at the base of some of the 

 lava-flows and rounded portions of lava in the beds of sandstone. 



It is important to notice that in all the occurrences cited in the 

 last paragraph the intercalation of sandstone and volcanics occurs 

 aliove the main mass of the Cave Sandstone; also that the sandstone 

 in this upper portion of the formation is usually well laminated. 

 This fact, coupled with the occurrence of pipe amygdales in the lavas 

 where these rest on the sandstone, seems to show that the conditions 

 of deposition of the sandstone were somewhat different from those 

 of the main mass and were somewhat moister and less arid. How- 

 ever that may be, it is apparent that the Cave Sandstone was not 

 deposited uninterruptedly: in places the deposition was hindered by 

 outbursts of ashes and of lavas from the many volcanoes of the area. 

 Du Toit remarks "While the Cave Sandstone accumulated freely in 

 the north and was followed by lava flows, the ejection of ash in the 

 south was so considerable that full development of the sandstone was 

 prevented in that region, and it was only at a slightly later period 

 that lavas commenced to be erupted there". 



The large Modderfontein volcano in Aliwal North came into existence 



