The physiography of Africa is essentially a reflection of the geologic history and geology that is described in the previous section. The continent, composed largely of a vast rigid block of ancient rocks, has geologically young mountains at its extremities in the highlands of the Atlas Mountains in the northwest and the Cape ranges in the south. Between these mountainous areas is a series of plateau surfaces, with huge areas that are level or slightly undulating, above which stand occasional harder and more resistant rock masses. Surrounding these surfaces is a zone of plateau slopes below which are narrow coastal belts widening along the Mediterranean coast, the coastlands of Tanzania and Mozambique, a narrow belt between the Niger and Cunene (Kunene) rivers, and an area northward of the Gambia and Sénégal rivers.
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Summit of Kilimanjaro, northeastern Tanzania.
The higher areas of the south and east are in marked contrast to the considerably lower elevation of the western and northern parts of the continent. South of a line drawn from near the mouth of the Congo River to the Gulf of Aden, most of the land lies 1,000 feet or more above sea level, and much of it exceeds 3,000 and even 4,000 feet. North of the line there is relatively little land above 3,000 feet, most of the area being between 500 and 1,000 feet above sea level; there are also broad coastal lowlands, except in the region of the Atlas Mountains and, in the east, beyond the Nile.
Afromontane moorland of tussocky grasses, giant groundsel, and lobelias on the slopes of Mount Kenya.
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To the north and west of the plateau area of the southern parts of the continent there is a general descent to the lower areas of the basins of the Congo, Niger, and Nile rivers. The only large areas that extend above 3,000 feet are in the folded ranges of the Atlas Mountains and in the central Sahara, where resistant granites form the massifs of Ahaggar and Tibesti. The interior uplands of western Africa and of Cameroon consist of ancient crystalline rocks, reaching considerable heights only in the Fouta Djallon plateau in Guinea, in the Guinea Highlands, which also extend over the borders of Sierra Leone and Liberia, in the Jos Plateau in Nigeria, in the Adamawa region of Nigeria and Cameroon, and in the Cameroon Highlands. There are extensive low-lying areas near the coast and in the basins of the Sénégal, Gambia, Volta, and Niger–Benue rivers. The high areas of Darfur in Sudan (more than 10,000 feet) and of Mount Cameroon (13,435 feet) are volcanic in origin and are evidence of the same tensions that have resulted in rifting and volcanism in East Africa.