Introduction 



of the main Nile ; and the black rhinoceros extends its range 

 — seemingly — into Eastern Nigeria (though not to the west 

 of the Niger) ; and according to the Roman records, was once 

 very abundant south of the Sahara, round Lake Chad. 



The vast forests of Central Congoland, south and west 

 of the main stream, are to-day very different from the Northern 

 Congo basin, the Cameroons, and the Tanganyika region in 

 their mammalian fauna, different in what they lack rather 

 than in what they possess. They are apparently without 

 anthropoid apes, giraffe or okapi, water chevrotain, and most 

 of the antelopes, the Hylochcerus pig, rhinoceros, zebra or 

 the Manis edentates (except the wide-spread Maw^'s temmincki), 

 and seemingly lack the aardvark. 



The reason for this poverty in mammalian fauna seems 

 to have been that within Pliocene and Pleistocene times, 

 when the rest of Africa was being peopled with the mammals 

 and birds of Europe and Asia, the Central Congo basin was 

 a vast fresh-water lake of which Lakes Leopold II and Man- 

 tumba are tiny residuary fragments. This question has been 

 treated at some length in my work on Grenfell's explorations, 

 so it is not necessary to descant further on it here. 



Similarly, and also within the human period, much of 

 the Sahara and Libyan deserts was under water ; so that the 

 routes by which tropical Africa received its modern mammals 

 and its early types of man from the Mediterranean lands 

 and from Western Asia were virtually restricted to the elevated 

 strip of the Tasili-Tibesti highlands from Algeria to Darfur, 

 and the mountainous country east of the Nile, from Egypt 

 to Abyssinia and East Africa. Much of the Bahr-al-ghazal 

 basin between Wadai and the vicinity of the Mountain Nile 

 was a vast shallow lake. 



xxxii 



