146 THE DESICCA-TION OF AFRICA. 



which is now beheaded, and its natural head-waters find an 

 outlet through the Blaauw Krans gorge. The deviation is 

 the effect of headstream erosion; the fact that a stream flowing 

 eastwards in a natural valley made for it should turn abruptly 

 at right angles and pierce a high range of quartzite hills, can 

 have no other explanation, unless we have recourse to faults, 

 of which there is no evidence. 



The coastal rampart of hills on the east coast, or on the 

 Gold Coast, is similar to that of the Grahamstown mountain 

 ridge, or Zuurberg. Substitute for the three streams, the 

 Kariega, the Kowie and the Blaauw Krans, the Sanaga 

 (Cameroons), the Ogowe and the Congo, or the Bandama, the 

 Volta and the Niger, and we see on a large scale what has 

 happened on a small scale near Grahamstown ; this fact, the 

 capture of the inland water-system by the smaller, but more 

 vigorously-flowing coast streams, is the great fundamental fact 

 which explains the alterations gomg on in the physical 

 conditions all over Africa. 



I have referred to the phenomenon of headstream erosion 

 in the Grahamstown hills because I happen to live m that 

 town, and the example is compact and complete, but quite as 

 good examples occur in the western mountains, especially 

 north of Ceres and generally throughout Cape Colony. In 

 Oudtshoorn there is a further example of two parallel rivers, 

 the Olifants, running in soft Cretaceous rocks, and the 

 Kammanassie, running in comparatively hard Devonian slates. 

 Here we have the conditions represented by the Niger, which 

 flows in Cretaceous strata above the Bussa Falls, and its 

 tributary, the Kaduna, which, originally probably of equal* 

 extent to the Niger itself, having to erode its bed m hard 

 granite, progressed but feebly, while the Niger spread back 

 and absorbed the whole of the drainage behind the coastal 

 rampart. The Olifants River has similarly spread back and 

 worn for itself a great alluvial plain, while the Kammanassie 

 has lost much of its original drainage area and lies in a 

 narrow valley. 



The topography of Europe, Asia and Africa was laid down 

 in the Eocene epoch. At the end of the Cretaceous period" 

 enormous changes took place ; the whole fauna of the world 

 was wiped out and new forms took their places. Among 

 vertebrates, for instance, the predominant type in the Cretace- 

 ous period was that of the reptiles, and in the Eocene the 

 modem mammalian types were introduced. Africa, which up 

 till then formed one continent with India, was riven by 

 gigantic faults, and the trough of the Indian Ocean was 

 produced. Round this fault-block the continents of Europe 

 and Asia became ranged, with the Alps-Himalayan chains as 

 the backbone. The destruction of life was related to these 



