Tlie Volcajwes of Griqualand East. 99 



there is a great diversity in the character of the agglomerate or 

 mixed-up material in the pipes. In the diamondiferous pipes, and 

 similar ones in the west, and also in the Bingara diamond pipe in 

 New South Wales, the agglomerate consists principally of the debris 

 of very basic rocks, which are not known to occur in situ in South 

 Africa, whereas the volcanic pipes of Griqualand East are filled in 

 with material usually with a very high percentage of silica. 



One fact makes the Griqualand East volcanoes of special interest. 

 They are very old, belonging to the upper Jurassic or Cretaceous 

 periods. Old volcanoes like these are known from many parts of 

 the world, and many midway in age between these and recent ones ; 

 but in these foreign ones either all traces of surface features are 

 entirely swept away by the long -continued action of wind and 

 weather, and we have only a hardly recognisable stump remaining ; 

 or, like in the Eifel, the whole cone is covered in by sediments and 

 the surface features are preserved while the internal structure is 

 hidden. In Matatiele, however, we get these stumps, and can see the 

 condition of things in the pipe many thousands of feet below what 

 was once the orifice of the volcano, but we can also trace some of 

 the surface features as well, and in one instance one can actually see 

 the lava still in continuity with the mass of molten material in the 

 pipe, pouring out over the surface of the old land-surface, and can 

 trace the ropy surface which the viscid liquid acquired as it cooled, 

 in days when the highest living being was a reptile. In this way 

 one has, by piecing together the evidence from two or three closely 

 adjoining vents, a natural section of a volcano of 4,000 or 5,000 feet 

 in vertical extent. 



A volcano either pours out liquid lava or throws out dust and 

 ashes, or does both alternately. Among the Matatiele volcanoes one 

 can find all three varieties ; that is to say, some of the vents are 

 filled almost entirely with solidified lavas, forming immense plugs ; 

 others are cylinders of dust and ashes, long consolidated into com- 

 pact rock, while other pipes again are filled in with varying propor- 

 tions of both. Of course one and the same volcano under different 

 circumstances may play both parts at different times ; a volcano 

 may for centuries continue to quietly pour out lava, and then of a 

 sudden enter on an explosive stage. From the fact that all the 

 Matatiele pipes, with one possible exception, contain some ash or 

 agglomerate, it is highly probable that the last stage of the volcanoes 

 was an explosive one, whatever kind of activity they previously had. 



It will be noticed that all these vents discovered in Matatiele 

 occur south of the Drakensberg range, and at first sight it would 

 seem that these volcanoes confined their attention to the northern side» 



