THE KARROO SYSTEM 231 



stone and ash, while abed of the latter about half a mile 

 north of the volcano contains large oval masses of lava, 

 apparently bombs which were ejected during one of the 

 eruptions. The Belmore volcano shows signs of repeated 

 activity and in great likelihood had a long life. 



Dykes of Karroo dolerite cut through a number of the 

 necks in Elliot and Wodehouse and occasionally traverse 

 the lava-flows as well. In this area there are no great 

 fissures through which the lavas may have reached the 

 surface. 



Prof. Schwarz, however, came to the conclusion that 

 some of the flows in Matatiele issued from fissures which 

 are now filled with dolerite and are dykes cutting both 

 the sedimentary rocks and the lower lavas. 1 The largest 

 of these dykes is about fifteen miles long and a mile wide 

 at its broadest part. It runs parallel with the main 

 ridge of the Drakensberg from Deer Park to George 

 Moshesh's country, and on its southern side the amyg- 

 daloidal lavas cut through by it are turned upwards in 

 a similar manner to the upturning of sedimentary beds 

 round the walls of a volcanic neck. Along the northern 

 wall of this dyke the lavas are much disturbed and 

 crushed. These are features which have not been 

 noticed in the usual dolerite dykes in the Colony ; in the 

 latter the molten rock seems to have risen quietly with- 

 out having to exert a force capable of crushing or dis- 

 turbing the rocks forming their walls. The formation 

 of the dolerite -filled fissure on the Drakeasberg ridge was 

 evidently accompanied by explosive action, and through 

 it may have been poured a large part of the lava which 

 1 Q. C., vii., p. 48, 



