3o8 PHYSIOGRAPHY. [chap. 



Africa (11,290,030 square miles, CXXV.), as already re- 

 marked, may be regarded as an appendage to Eurasia. In 

 historic times, the pnly connection has been with Asia by 

 means of the Isthmus of Suez ; but there are good reasons 

 for believing that, even in post-tertiary times, Africa must 

 have been also united with Europe ; the connection having 

 been effected across what is now the Strait of Gibraltar ; and, 

 also, by means of land which stretched over to Italy, and of 

 which Malta and Sicily are points still above water. In the 

 northern part, Africa has rather an east-and-west extension, 

 like that of Eurasia. And, though it has no general axis 

 of elevation ; yet, such mountains as it does possess, have 

 a tendency to stretch in the same direction. This is seen, 

 for example, in the Atlas mountains in north-western Africa, 

 and in the Kong mountains parallel with the northern 

 shores of the Gulf of Guinea. The southern part of the 

 continent extends, on the contrary, in a north-and-south 

 direction ; and the elevated lands of Abyssinia and Zan- 

 guebar follow the same course. 



One of the most striking physical features of Africa is 

 the great northern plain which forms the desert of Sahara. 

 This has an area fifty times as large as that of Britain, 

 depressed in some places below the sea-level, but rising, in 

 others, to 2,000 feet above it. From the occurrence of 

 marine shells in the superficial deposits, and for other reasons, 

 it is believed that the Sahara is an old sea-bottom, which 

 must have been below water at a comparatively recent 

 geological period. The proposal to admit the waters of 

 the Mediterranean artificially into the depressed portions of 

 the desert has been seriously entertained. 



Regions of inland drainage may be found in some of the 

 table-lands in the heart of Africa. Lake Tchad, for example, 

 is a shallow sheet of water which receives the drainage of 



