268 PEOF. A. H. GEEEX OX THE GEOLO&T AJTD 



ingh' we find there the Ecca Beds, Dwyka Conglomerate, and 

 Quartzites folded in among one another in sharp and closely packed 

 convolutions. But the contortion diminishes rapidly in intensity as 

 we go northwards, the folds open out, and the Ecca Beds soon come 

 to lie in a succession of broad rolls, though among these closely 

 compressed arches with steep dips are not uncommon. 



The next scene introduces us to a very long period of steady 

 depression, by which a large freshwater lake was formed. In this 

 lake the Kimberley Shales, Karoo and Stormberg Beds, Bed Beds, 

 and Cave Sandstone were laid down in conformable succession. 

 During the formation of these beds volcanic forces seem to have 

 been gathering head underground. Probably they did not succeed 

 in forcing open roads to the surface during this long period, for no 

 contemporaneous lava-flows are known in any of the above-mentioned 

 groups. But doubtless, before any subaerial outburst took place, 

 lava was actively burrowing about underground; and we may 

 reasonably suppose that many of the intrusive sheets and dykes 

 that abound among these rocks were injected while the beds 

 among which they occur were in process of formation, and when 

 there was only a small thickness of rock overhead to oppose their 

 motion. We can thus explain the very trifling amount of disturbance 

 which the intrusive masses produce in the rocks which they 

 traverse. 



But after the formation of the Cave Sandstone, the pent-up lava 

 burst its way up to day, and great flows and beds of tuff bespeak a 

 period of volcanic eruptions. Of its products, denudation has left 

 us only the merest shreds, but these occur scattered over so wide 

 an area as to leave no doubt that the outbursts must have been of 

 no small magnitude- 

 It often crossed my mind, as I vainly endeavoured to number up 

 the sheets and dykes I had come across in the course of a day, that 

 it is only in a country like this that we can form any adequate 

 estimate of the underground work of volcanic forces. Over an area 

 certainly 120,000 square miles in extent, and probably much larger, 

 dykes, sheets, and huge masses of trap meet one at every turn. 

 Sometimes, as for instance near Burgersdorp, there are tracts in 

 which you may go for several miles and see nothing but trap, so 

 close together do the intrusive masses run ; elsewhere they are more 

 scattered, but no part of the area is free from them. 



The upheaval that finally lifted the rocks last described into the 

 air must have been of a gentle character ; for they are but very 

 slightly disturbed from the horizontal. Since it took place South 

 Africa has probably continued dry land down to the present day ; 

 for the scraps of Jurassic, Cretaceous, and Tertiary formations that 

 it possesses lie close to the coast and apparently were formed at no 

 great distance from the shore. During this long period subaerial 

 denudation has had ample time to clear away the many cubic miles 

 of rock that must have been removed to form the present surface. 



A certain similarity between the scanty fossils of the Karoo Beds 

 and the almost equally scanty faima and flora of the Lower Gond- 



