xv The Continental Area 289 



flow. The Basin is divided by the Flinders Range west of 

 the Murray, and its western part forms a depression scarcely 

 raised above sea-level, in which lie Lake Torrens and Lake 

 Eyre salt lakes with no outlet. The whole depression is 

 rimmed round with coral limestone of Tertiary age, and 

 appears to have formed a wide shallow bay long after the 

 rest of the continent was upheaved. The plateau to the 

 west is a great desert not fully explored, and composed of 

 the rock known as desert sandstone, fringed to the south 

 by grand cliffs of tertiary limestone which line the Great 

 Australian Bight as a wall about 400 feet high, unbroken 

 by a single river for 1000 miles. 



373. Africa presents a typical triangular outline resem- 

 bling that of South America, but the north-western outcurve 

 is much more pronounced, while the north-eastern outcurve 

 is broken by the depression of the Red Sea. Round Africa 

 the Continental Shelf is extremely narrow, and the islands it 

 bears are few and small, while the coast-line is less indented 

 than that of any other continent. The greatest length, 

 nearly 5000 miles, lies along the central meridian of 20 

 E., and the" greatest breadth, 4500 miles, is on the parallel 

 of 10 N. Africa is the only continent crossed by both 

 tropics, the equator passing nearly through the centre. 

 The average elevation of Africa is nearly that of all the 

 land ; but no other continent has such a small proportion 

 of land below 600 feet in height (one-eighth of its area), 

 and none has so great an extent (nearly two-thirds) between 

 the heights of 600 and 3000 feet. 



374- Slopes of Africa. A section drawn across the con- 

 tinent, along the equator (Fig. 61) hardly shows how com- 

 pletely the typical continental structure is departed from, as 

 Mount Kenia is only an isolated peak, not part of a range. 

 All the rivers pursue singularly curved courses, unlike those 

 of any other continent, and where they drop over the edges 

 of the plateaux form great cataracts. The watersheds are 

 not dominated by mountain ranges, but by the broad backs 

 of plateaux, out of which the main features of the land- 

 slopes have been carved by erosion. The Atlas moun- 

 tains run along the coast in the north-west and rise 



U 



