In December, 1987, Project 233 of the International Geological Correlation Pro gram hosted an international conference in Nouakchott, Mauritania. Discussions were focused on the "Tectonothermal Evolution Of The West Mrican Orogens And Circum-Atlantic Terrane Linkages". A wealth of new information was pre sented during the conference, and it was apparent that the time was appropriate to prepare a systematic volume dealing with the geology of northwest Mrica. The present volume is an outgrowth of this conference, but is not merely a compilation of the papers presented in Nouakchott. Instead, it represents a coordinated vol ume designed to present a balanced, comprehensive view of our present under standing of West Mrican geology and potential correlations in other Circum-At lantic Paleozoic orogens. We sincerely appreciate the efforts of all the reviewers whose comments have greatly helped to improve the quality of this volume. We also thank the various contributors for their diligence and perseverance in manuscript preparation. The calibre of the present volume is a reflection of their labor. Athens/Marseille, Autumn 1990 R. D. DALLMEYER J. P. LECORCHE Contents Chapter 1 Introduction . . . . . . . . . . . . . . . 3 R. D. DALLMEYER and J. P. LECORCHE Chapter 2 Geophysics and the Crustal structure of West Africa 9 J. ROUSSEL and A. LESQUER Chapter 3 Crystalline Basement of the West African Craton . . . . . . . . . . . . .. . . 31 .