The appearance and characteristic features of landforms are greatly influenced by the underlying rock type. Softer rocks like clay and shale are worn down much faster than harder rocks like granite.
The ancient rocks which dominate a great part of West Africa have been so greatly worn down by erosion that they now appear as peneplains. Granite domes for inselbergs have been formed where the old rocks resist erosion: and in some cases, such resistant high rocks produce high relief, such as the Jos Plateau of Nigeria, the Akwapim-Togo-Atacora ridges and the Birrimian uplands of Ghana, and the interior plateaux and mountains of Sierra Leone, Shales, schists and sandstones, being less resistant, form the much lower, rounded hills. Recent river sediments form flat plains.
Volcanic activities in some parts of West Africa had produced landscapes of high elevation such as the Cameroon Mountains; the Cameroon and Bamenda Highlands; the Jos Plateau of Nigeria; Cape Manuel, Goree and the Mamelles of Cape Verde. The islands of Fernando Po, Principe, Sao Tome and Annobon contain similar high reliefs too. The Sierra Leone Peninsula, which was formed from the basic intrusive rocks, now has erosion platforms of varying heights, whilst Cape Mountain of Liberia is another relief feature formed from Pre Cambrian (basic) intrusive rock.
Impressive scenic features in the form of gorges, scarps, etc., have been produced where running water and other agencies of denudation have heavily dissected or cut through the basic rocks. Such features are commonly seen on the Fouta Djallon Highlands of Guinea, and the scarps of Mali, south-western Burkina Faso and Mampong of Ghana, Limestones, resistant because of their permeability, form prominent steep sided hills such as those near Ipoh and in Perlis near Kuala Lumpur, Malaysia.
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