One of the more stimulating aspects of working in the field of African studies is the co-operation between scholars of related disciplines such as is not always found among those working in other parts of the world. Historians have been outstanding in promoting this co-operation and it was therefore gratifying to read Michael Mason's paper in the Journal, in which he uses and comments upon the work of geographers in developing his thesis that the Middle Belt of Nigeria may have been an area of sparse population before slave raiding during the nineteenth century. His paper is well documented, closely argued and apparently authoritative. However, there are several points on which we would take issue with Mason, some of which are so fundamental that it would be unfortunate in our view if they were absorbed into the historical literature unchallenged. It is not our purpose in raising these matters to spark off a fruitless ‘intertribal’ war; it is rather to offer constructive criticism to the advantage of historians, geographers and others.