Readers of the accounts by the great naturalist explorers of the later eighteenth and early nineteenth centuries are often impressed by the acuteness of observation displayed, and even more often by the variety of the phenomena described. Since the day of these pioneers every one of the aspects of Nature and of Man about which they wrote has become the field of a separate branch of science, and each decade sees new shoots emerge with the accelerated specialization of science and its researches. With the rapidly increasing means of publication all these extensions of knowledge contribute to a literature so vast that no individual can follow it over the domain of even one of the major divisions, whether of Earth lore or the social sciences. The appearance, then, of any form of authoritative book which provides a conspectus of existing knowledge in a given field is welcome. When the field is a continent, or any geographical unit, we are generally better off than usual in this respect, since the function of geography is both analytic and synthetic and above all is correlative; for Africa, indeed, excellent general geographical treatises exist in at least three languages.