102 Transactions of the South African Pliilosophical Society. 



nature of the hill as being of volcanic origin, but on the north side 

 there is a thin flow of amygdaloidal lava passing from the pipe 

 towards the great mass of lava that forms the mountain-crest 

 behind ; the lava-flow w^as the first that occurred in this region, for 

 it can be traced underlying all the others in the escarpment at the 

 top. This first flow is covered near the vent by two or three others, 

 but at one place the latter have been weathered away, leaving a 

 shelf which shows the actual surface of this first flow. The surface 

 has the peculiar structure known as ropy, and is that which any 

 viscid material acquires when allowed to flow slowly, and can be well 

 seen in pitch that oozes out of a broken barrel. The ropy surface, I 

 take it, is a proof that the lava was poured out on the surface of the 

 ground, and not under the sea as has been suggested, as it is unlikely 





FiCx. 1. 



View of the high volcano on Deer Park, seen from the west. 1. Plug of 

 columnar dolerite. 2. Cave sandstone forming a rim round the plug. 3. Amyg- 

 daloidal melaphyre forming the crest of the Drakensberg. 3a. A portion of a 

 flow of amygdaloid which has evidently come from the vent, and which passes 

 beneath the rest of the lavas on the north ; at one place this flow shows the ropy 

 surface of cooled lava. 4. A small tract of volcanic agglomerate with vesicular 

 bombs and fragmental sedimentary rocks. The stipling represents the grass- 

 covered slopes. 



that such a structure could be formed under water with considerable 

 pressure to add to the fluidity of the molten rock. The thickness of 

 these three lava-flows that can be seen near the vent are remarkably 

 thin, being only 1 foot to 3 feet in thickness, while there are small 

 flows wedged in between the principal ones that are hardly a foot in 

 tliickness. 



