The Influence of Rock Types on Landscapes

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.

Metamorphic Rocks

All rocks whether igneous or sedimentary may become metamorphic or changed rocks under great heat and pressure. Their original character and appearance may be greatly altered by such forces, particularly during intense earth movements. In this manner, clay may be metamorphosed into slate, limestone into marble, sandstone into quartzite, granite into gneiss, shale into schist and coal into graphite.