RESEARCH IN BRITISH WEST AFRICA. 305 



points will, therefore, be kept prominently in view in this report when the writer 

 is considering in detail the various regions visited. 



(b.) Mountain and River Systems. 



A sketch map (PI. VII) has been added to ilkistrate the general contour and 

 the river systems in the Protectorate, so that it is necessary here to draw 

 attention only to the major features. The dotted contour lines indicate the 

 average level of the various regions in the country, and from these it will at once 

 be seen that the general altitude is not great. 



The Bauchi plateau, the highest part of the Protectorate, is only between 

 4,000 and 5,000 feet above sea-level, and forms the central watershed of the 

 Protectorate, whereas Lokoja, 337 miles, and Jebba, over 600 miles from 

 the sea, are respectively only 300 and 500 feet above sea-level ; so that the 

 general fall of the river is only about one foot per mile. 



There are two main river systems in Northern Nigeria ; first the inland 

 system which drains into Lake Chad in the north-east corner ; and 

 second, the Niger-Benue system, with its outlet to the sea through Southern 

 Nigeria. 



(1) Lake Chad is a lake only in name, and consists of nothing but an immense 

 marsh with variable stretches of open water nowhere more than twelve 

 feet deep. 



The basin of Lake Chad lies curiously between the watersheds of the Niger 

 and the Nile, and is supposed to be the remains of a vast shallow inland sea 

 which covered most of the region north-east and west of the present lake, and 

 which probably communicated with the sea along the basin of the Senegal River. 

 A recent French expedition has shown that, at any rate in the rainy season of 

 one particular year, there was a continuous water connection between the Benue 

 and Lake Chad through the Tuburi marshes into the Logun river, and thus into 

 the Shari river, which runs into the Lake. This being so, the lake was tke?i 

 nothing but a backwater of a river system in Central Africa, which sent a super- 

 fluity of its waters to the Benue and the Niger. 



But, apart from this, Lake Chad merits attention here from the fact that it 

 drains roughly one quarter of the Protectorate of Northern Nigeria (the north- 

 east portion), and, as will be seen later, is of great interest in connection with the 

 distribution of the various species of Ghssina. 



(2) The Niger-Benue system drains the rest of the Protectorate — the Benue 

 the south-eastern quarter, and the Niger the western half. 



There are two primary watersheds in the Protectorate itself, and these radiate 

 from the Bauchi Plateau, the first north-west, and then north-east to the French 

 Sudan near Katsena, the other north-east and then south-east to the Kamerun 



