THE KARROO SYSTEM 223 



several localities where the volcanic rocks rest uncon- 

 formably upon the sedimentaries. 



In the western part of Elliot, under Xalanga Peak, the 

 lowest lavas rest upon the Cave sandstone for a certain 

 distance and then pass downwards at a moderate angle 

 over an apparently eroded surface of that rock until they 

 rest directly upon the Eed beds. To the north-east 

 there is a band of red sandstone and shale rather under 

 fifty feet thick intercalated between the lower groups of 

 lavas for a distance of some ten miles round the head- 

 waters of the Qokama River. The lava below the Red 

 sandstone band lies upon the Red beds. At Siberia, 

 some distance to the north-west, the Cave sandstone 

 has suffered faulting and erosion prior to the outpouring of 

 the lavas ; above the main bed of Cave sandstone in this 

 locality there are three other sandstone bands interbedded 

 in the lavas and traceable for considerable distances. 



In Barkly East this alternation of sedimentary and 

 igneous material is very marked, and the history of the 

 eruptions can in consequence be worked out in detail by 

 following up these thin and often remarkably regular 

 intercalations of sandstone and tuff. 



The presence between lava-flows of sedimentary 

 material, frequently passing both vertically and laterally 

 into volcanic ash, the presence of masses of lava (bombs) 

 embedded in fragmental rocks, and the layers of pipe- 

 amygdaloid at the bases of the individual lava-flows, all 

 indicate that the earliest volcanic eruptions took place 

 under water. The outbursts of molten rock must have 

 been followed by intervals during which sedimentation 

 proceeded more or less continuously. 



