The Forming of the Drakensherg. 65 



double that length. The immense number of horizons at which the 

 pipe-amygdaloid occurs in this area — sometimes over a dozen are 

 present in a vertical distance of a few hundred feet — shows that the 

 lava usually flowed over a wet surface. When we add to this the 

 fact that we get numerous thin beds of usually well-stratified sand- 

 stone and ash between the lavas, it will be seen that the evidence 

 for the sub-aqueous eruption of the lavas is very strong. In the 

 Barkly East Division the history of volcanic activity can be made out 

 with considerable detail, whereas in other areas we find only a 

 succession of lava flows from which nothing much can be learnt. 



We have seen that, at the close of Cave sandstone times, there 

 existed a vast shallow lake or sea, with a sandy bottom. 



The first evidence of the pent-up energy below the crust of the 

 earth is shown by faulting in the rocks on the eastern border of 

 Wodehouse. These faults must have been formed by earthquakes 

 which heralded the volcanic outbursts. 



The strata bulged up in places and the currents rapidly removed 

 the obstructions, so that occasionally the whole of the Cave sandstone 

 was carried away before the first eruptions occurred. 



Thin, irregular lava flows interbedded in the Cave sandstone 

 indicate the birth of the earliest of the Drakensberg volcanoes. 

 They were immediately followed by others, and lava streams 

 flowed over the bed of the lake, while ash and volcanic bombs 

 were occasionally ejected. 



Along the Kraai Eiver valley the bed of the lake subsided in two 

 separate areas, and lava was rapidly accumulated. Whenever an 

 eruption diminished in vigour sediment was deposited, and a bed of 

 sandstone formed. In many cases the upper surface of the under- 

 lying lava was cracked and fissured, and into the spaces silt intro- 

 duced itself. Some of these veins of sandstone have been baked to 

 quartzite, showing that the central portion of the lava flow was still 

 at a high temperature. Ash and masses of molten material were 

 flung into the air from the craters, and became embedded in the 

 still soft sediment. Many of these masses of lava are several feet 

 across, and must have been in the molten state when they fell into 

 the soft mud, for their lower surfaces show rows of pipe amygdules 

 arranged normally to their bases. Some of these blocks have been 

 ejected a distance of certainly over half a mile from the nearest 

 known crater. 



Such were the preliminary volcanic outbursts in the area, but they 

 were apparently dwarfed by the eruptions which followed. Scores 

 of volcanoes came into action apparently almost simultaneously, 



5 



