THE DESICCATION OF AFRICA. 147 



convulsions in the earth's crust, and we can reconstruct from 

 geological evidence a picture of what then went on. The 

 earth's crust was disturbed, was broken and crumpled, as if a 

 blow had been given it and the material were plastic like 

 modelling clay. The convulsions were not confined to a single 

 short period, but were spread over what would be regarded 

 historically as an immense stretch of time, and at the end 

 the world-segments, the continents and oceans, emerged more 

 or less in the broad outlines in which we now see them. The 

 movements continued during the Eocene period and altered 

 somewhat the original plan, but we can regard these as 

 supplementary. As a matter of fact, the barriers raised by 

 these later movements are definitely athwart an earlier 

 topography, and the rivers with which we are chiefly concerned 

 are busy removing them and restoring the earlier features. It 

 is on this assumption that the reasoning in the following pages 

 is based, but it would take us- too far from the subject in 

 hand to develop it fully. To put it concisely, the features of 

 the earth's surface, its topography, its rivers, hills, coast-lines, 

 etc., date from the dawn of the modern period, the Eocene; 

 these were on a different plan and had no relationship to the 

 topography of the earth's surface in earlier periods. That, in 

 the widest sense, is a sort of master-key to the understanding 

 of the present condition of affairs, and the changes that are 

 now going on are alterations of that original Eocene plan. 

 Individual terrains, when examined in detail, confuse this 

 prime conception, because we may find that the original 

 topographical features were laid down later than the Eocene, 

 or, may be, earlier, as in Cape Colony, and it would be more 

 strictly accurate to leave the period in which the stamp was 

 set indefinite : that a stamp was set and that its recognition 

 explains why the conditions in various countries are changing, 

 we shall see ample evidence in the sequel. 



THE NIGER. 



The Niger rises m the granite hills of Tembi Kundu, 

 2,764 feet above sea-level. These hills form part of 

 the coastal rampart which guards access to the interior 

 from the sea on the Gold Coast and which, indeed, is a 

 characteristic feature on the whole west coast as far as 

 Cape Colony. It is deeply canyoned on the sea-ward side 

 towards Sierra Leone and Liberia and the main watershed 

 has retreated inland under the action of headstream erosion 

 by the short, rapid rivers of the coast. Some of the heights 

 of the original crest, like Mt. Drouple, 9,750 feet, are left 

 isolated and far south of the watershed- 



On the north, the Tankisso River, flowing from the sand- 

 s,tone hills of Futa Jallon, joins the Niger at Siguiri, which is 



