Although our present knowledge of British Guiana— particularly in detail and in the southern part of the country—is far from complete, it appears timely to attempt a synthesis of some of the major facts that are known. The following account seeks to summarize some of the more pronounced features of form and structure; it raises the question of a large discontinuity or break from south to north along the course of the greatest river—the Essequibo; it seeks to interpret the meaning of the contrasted river-systems west and east of the Essequibo; it raises the question of subsidence in the Berbice Valley, and of the early Amazon drainage; and discusses the problem of continental drift from Africa in the light of du Toit's criteria.