The geological basement of the central and eastern regions Equatorial Guinea is composed of Precambrian rocks which form a part of the Congo craton. They include gneiss, greenstone, schist-amphibolite and granitoids. These older rocks are overlain by sedimentary rocks of Mesozoic, Neogene and Quaternary age in the west and along the coast. The islands of Pagalu and Bioko (Annobon and Fernando Poo) are of relatively recent volcanic origin, forming a part of the Cameroon Volcanic Line.