548 F, P. Ilennell — Two Points in African Geology. 



who have preceded him. There is always a great disposition ou 

 the part of visitors to a little-known country to theorise, without 

 having had time or opportunity for making those accurate and 

 detailed observations which are essential if deductions are to be 

 made which will stand the test of time. And the worst of it is, 

 'authority ' has so much weight that local workers have the utmost 

 difficulty in removing false impressions which may thus be caused. 

 Two points to which I may refer are the " antiquity of the African 

 continent" and the so-called ' Eift- valleys.' Now whatever may 

 be the antiquity of Africa as a land surface, facts are constantly 

 coming to light which throw great doubt on its having the stability 

 attributed to it. Fossils of Jurassic and Cretaceous age are known 

 from numerous places, and though these are chiefly confined to the 

 coastal fringe, fresh discoveries are frequently increasing the area, 

 such as the recent one far inland in the Sahara. Further, though 

 the absence of marine fossils — or, rather, of any fossils at all — from 

 the sandstones which cover immense areas in Tropical Africa may 

 be held to denote a lacustrine origin for the beds, it is quite possible, 

 as Mr. Moore seems to take for granted, that they may be marine. 

 They are largely red sandstones with intercalated lavas (basalt, etc.), 

 and extend from the edge of the African plateau on the east to its 

 western limit, and from the Limpopo to the Equator or near it. 

 These beds are involved in the mountain-building on the south-east 

 border of Ehodesia, and it thus appears possible that no mountain 

 barrier originally existed along the east coast. Indeed, I believe the 

 beds reach down into the low country near Sofala, where Cretaceous 

 fossils occur. These red sandstones are particularly well developed 

 in the Congo basin and the Zambesi basin. Mr. Moore calls them ' 

 the " Old African Sandstones," and considers that they underlie 

 " Drummond's Beds." There must be some mistake here, as the 

 latter no doubt correspond to the Permian coal-beds of Rhodesia, 

 while the sandstones are what I have tentatively classed as of 

 Tertiary age," and extend almost continuously through Ehodesia 

 from Lake Tanganyika to Bulawaj^o. 



But, granted that these beds are non-marine, the freedom of the 

 continent from extensive earth-movements does not rest on any 

 sounder basis. The beds are largely involved in erogenic move- 

 ments, not only round Lake Tanganyika, but also in Southern 

 Ehodesia, and frequently dip at considerable angles. The great 

 volcanic activity that they evidence is another point against stability. 

 But the strongest argument is the insignificant amount of denudation 

 accomplished since the great plateau has been raised to its present 

 elevation of about a mile above sea-level. We have gently 

 undulating or flat country with deeply scored valleys ; the streams 

 are as yet simply torrents employed in deepening their beds. They 

 have not begun to aifect the general level of the country, while falls- 

 and rapids are of frequent occurrence even in the great rivers, an 



' " The Tanganyika Problem," p. 65. 

 ^ Ann. Eep. Ehodesia Museum, p. 9. 



