PALEOZOIC ICE-AGES OF SOUTH AFRICA 689 



A typical section of the shale band on the Clanwilleain side of the 

 Cederbergen gives: 



Shale 200 feet 



Shaly conglomerate 20 feet 



Conglomerate 100 feet 



The conglomerate is a mudstone containing pebbles and bowlders 

 up to fifteen inches in diameter. The latter consist of quartz, three 

 distinct varieties of quartzite, sandstones, felspathic grits, diabase, 

 amygdaloidal melaphyre and granite, and are well faceted, and 

 the closer-grained ones strongly and characteristically scratched. 

 North of Clanwilleain, the Table Mountain sandstone rapidly thins 

 out, and the upper beds one by one drop out till, in Van Rhyn's 

 Dorp, the Dwyka Conglomerate is separated from the Pal-Afric 

 beds by only a few feet of quartzite, and in Bushmanland rests 

 directly upon them. There may be a locality where the Permian 

 glacial beds rest directly on the Devonian ones, but we have not 

 found such a one. Apart from stratigraphical evidence, it would 

 be extremely difficult to separate the two; the only difference we 

 could find — and it amounts to very little — is the presence of quartz 

 pebbles in the Table Mountain conglomerate. 



The area of the Devonian glacial beds is uncertain. The actual 

 outcrop from which bowlders have been obtained is 23 miles long, 

 but the ends plunge under debris and are certainly continued north 

 and south. Eastward the limb of the great Cederberg anticline 

 dips under the Karroo beds, so that it is uncertain how far the glacial 

 beds extend in this direction. We find bowlders of Table Mountain 

 sandstone -brought up from great depths in the agglomerates in the 

 Sutherland volcanoes, right in the deepest part of the Karroo sinking, 

 but we can naturally see nothing in them which would help us in 

 tracing the glacial beds. On the east, where the Table Mountain 

 sandstone comes again to the surface in Pondoland, we have not 

 been able to trace the shale band, nor have geologists recorded it in 

 Natal. 



At some future date it will perhaps be established that there is a 

 rhythmic recurrence of glacial conditions in subtropical and even 

 tropical countries, and we shall be able to date the rock strata accord- 

 ing to the positions of these tills. In Australia they have two — the 



