James MacQueen (1778–1870) was a British geographer fascinated by the problem of the River Niger. He set out to try to establish (on the basis of accounts by explorers, traders and missionaries), that one and the same river flowed continuously through Africa and into the Atlantic Ocean, thus challenging long-established beliefs that African rivers either disappeared into the sand or terminated in lakes. MacQueen documents his findings in this pioneering work, first published in 1821. Drawing on evidence from a range of authorities, he argues that previous misconceptions about the Niger had left Africa isolated from the civilised world, and shows how his discovery could open up trading opportunities between Africa and other countries, suggesting that contact with Europeans would lead to the eventual abolishment of the slave trade in the interior. This important study remains relevant to scholars of both geography and African history today.