Three themes run through this book, the first is the history of the Nile; the second is the degree to which the present Sudanese landscape reflects the operation of former geological processes; the third is the interaction between man and environment, not always to the benefit of either. A land between two Niles is an interdisciplinary account of the origins and characteristics of the alluvial plains of the lower Blue and White Nile. The contributors have focussed their attention upon this region for several reasons. Although the Gezira plain itself only occupies about one percent of the total area of the Sudan, the high quality long-staple cotton grown there provides nearly two-thirds of the country's total export revenue.