The geology of Nigeria could be described as Pre-Cambrian, Cretaceous, Tertiary, Quaternary and Volcanic. The pre-Cambrian rocks are made up of igneous and metamorphic rocks and cover almost fifty percent of the country. They are crystalline in nature and consist of granite, gneiss and schist and they are commonly referred to as the Basement Complex. When weathered, the older granites give rise to smooth-domed hills known as inselbergs. The Cretaceous rocks are relatively younger rock types than the Pre-Cambrian rock types. They consist of various sandstones that are basically classified as older sedimentary rocks. Cuesta relief forms are characteristic of these rocks; and coal, lignite and limestone are important minerals found in these rocks. These rocks occupy the basins of Niger, Benue, Gongola and Cross Rivers. The younger sedimentary rocks are the rocks of the Tertiary Age consisting mainly of sandstone but with some clay and lime- stone. They are found in the Chad Basin and in the South with its widest extent in the Lower Niger. The alternating layers of clay and sand, especially in the Chad Basin are a noteworthy characteristic of these rocks. The Quaternary rocks are comparatively recent depositions found along the coast and river deltas of the country. They are made up of sandy and muddy deposits. Volcanic rocks which are of the Tertiary Age are not wide- spread in Nigeria. They are mainly found in the centre and north-east of the country. The main areas are the Biu and Jos Plateau and the Kerrikerri area of the Benue valley. The acid and basic rocks of these places give rise to peculiar volcanic features.