Explanatory note on the Block Diagram of the Great Rift Valley from Nakuru to Lake Magadi (Plate XIV)

Abstract

This diagram was constructed during an examination of the Rift Valley region on behalf of the D'Arcy Exploration Company and the Anglo-Saxon Petroleum Company. The author is greatly indebted to these companies for permission to publish this work, and acknowledges with gratitude the assistance rendered during the examination by the Department of Mines, Kenya Colony. It is difficult to give an effective picture of the Great Rift Valley by contour maps, and in those that exist the topographer has tended rather to round off his contour lines in the conventional manner, so that, where in nature there exists bold ruggedness, there appears on the map only flowing curves. An attempt has been made in this projection to bring out the steepness of the fault scarps, and the colouring has been progressively deepened to show the increasing depth to which the plateau has been faulted down. Thus the plateau round Nairobi, lying on the Kapiti plains, is coloured lightly, and the depth of colour increases northward from Limuru along the Kainankop plateau, and then down to Naivasha. Yet Naivasha is at a greater height above sea-level than Nairobi, the sides and bottom of the Rift Valley having together been raised to the northward relative to sea-level. There is a considerable slope of the whole of the Rift Valley and its sides towards the south. Thus, Lake Magadi lies at the lowest point in the diagram, though the difference between the level of this lake and the sides of the valley is