Abstract The Austrian geomorphologist Eduard Suess was the first to recognize the importance of the African rift valleys. However, Suess never visited Africa, and he would never have been able to make his perceptive recognition of this aspect of the geomorphology of the African continent had it not been for earlier field explorers. The discovery of the African rift valleys can be traced back to the middle part of the nineteenth century. At the time, little was known about the interior of much of Africa, partly because, due to uplift of the continental rim, easy access to much of the interior of Central Africa was precluded by major cataract systems near the mouths of many of the larger rivers (Congo, Niger, Zambesi). The mainspring for the exploration of East Africa came from a largely unacknowledged source, the missionary community on the East African coast. In 1846, the Church Missionary Society of London established a mission station at Kisuludini in the Rabai Hills on the mainland across from Mombasa Island. The mission was started by Johann Krapf, who was soon joined by Johann Erhardt and Johann Rebmann. All three were Lutherans, trained at Basel; apparently the Society had difficulties recruiting British missionaries for the arduous mission life in East Africa ( Oliver 1952 ). In addition to their pastoral duties, the missionaries travelled inland in attempts to find suitable sites for further mission stations and, during these journeys, they made observations on the geographical features they encountered. It was on such journeys that Rebmann