The Rift valley, though with a generally level floor, is divided by transverse ridges into a series of basins, each containing a lake without outlet. The southernmost section within the col ony is formed by the arid Dogilani plains. At their north end rise the extinct volcanoes of Suswa (7,80o ft.) and Longonot (8,70o ft.), the latter on the ridge dividing off the next basin— that of Lake Naivasha. This is a small fresh-water lake, 6,135 f t above the sea, measuring some 13 m. each way. Its basin is closed to the north by the ridge of Mt. Buru, beyond which is the basin of the still smaller lakes Nakuro (5,845 ft.) and Elmen teita (5,86o ft.), followed in turn by that of Lakes Hannington and Baringo (q.v.). Beyond Baringo the valley is drained north into Lake Sugota, in N., some 35 m. long, while north of this lies the much larger Lake Rudolf (q.v.), the valley becoming here somewhat less defined.
On the west of the Rift valley the wall of cliffs is best marked between the Equator and I° S., where it is known as the Mau escarpment, and between the Equator and I° N., where the El geyo escarpment, finely forested, falls to a longitudinal valley separated from Lake Baringo by the ridge of Kamasia. Opposite Lake Naivasha the Mau escarpment is over 8,000 ft. high. Its crest is covered with dense forest. To the south the woods become more open, and the plateau falls to an open country, drained towards the Dogilani plains. On the west the cultivated districts of Sotik and Lumbwa, broken by wooded heights, fall towards Victoria Nyanza. The Mau plateau reaches a height of 9,000 f t. on the Equator, north of which is the somewhat lower Nandi country, well watered and partly forested. In the treeless plat eau of Uasin Gishu, west of Elgeyo, the land again rises to a height of over 8,000 ft., and to the west of this is the great moun tain mass of Elgon (q.v.). East of Lake Rudolf and south of Lake Stefanie is a large waterless steppe, mainly volcanic in character, from which rise mountain ranges. The highest peak is Mt. Kanjora, 6,90o ft. high. South of this arid region, strewn with great lava stones, are the Rendile uplands, affording pastur age for thousands of camels. Running north-west and south-east between Lake Stefanie and the Daua tributary of the Juba, is a mountain range with a steep escarpment towards the south. It is known as the Goro escarpment and at its eastern end it forms the boundary between Kenya and Abyssinia. South-east of it the country is largely level bush-covered plain, mainly waterless.
inland, older and older rocks are found until the gneiss zone is reached. This zone is very extensive ; on the line of the Kenya and Uganda railway it extends from mile 57 to mile 283. Coarse grained and well foliated, the gneiss is very uniform in structure. It is composed chiefly of quartz, felspar and hornblende ; mica is sometimes present. A bright red sandy soil is formed by the dis integration of the gneiss in its eastern border, which is arid and generally level but with characteristic isolated hills. Farther west the desert condition ceases, and black cotton soil is found in places. A series of mountain ridges—the crests of ancient earth folds 5,00o to 7,00o ft. high and 2,000 to 3,00o ft. above the normal level, run in a north-west to south-west direction. In the third or i highland zone, the gneiss is covered by a deep cap of lava, which extends over some 5o,000 sq.m. from the southern border north east to the frontier. Above this lava bed tower the extinct volcanoes of Kilimanjaro, Kenya, Elgon and the Aberdare mountains, while much of the Northern Frontier province con sists of lava ridges separated by stretches of stony desert. This highland region is traversed by the eastern Rift valley.
Volcanic activity preceded and followed the subsidence which caused the Rift valley to be formed. The older activity, starting apparently in the Cretaceous age, began with a series of fissure eruptions along the site of what afterwards became the Rift valley and also on both sides of the "valley." From these fissures issued immense and repeated flows of lava, burying the gneiss to varying depths. These fissure eruptions—the welling up of liquid magma— produced no craters. They formed vast plateau plains, such as the Athi and Kapati plains. In the Eocene age came another series of eruptions producing craters, such as that of Mt. Kenya and the Marwenzi crater of Kilimanjaro, and after the Rift valley had been formed there was a further period of volcanic activity, as witness Longonot, in the Rift valley, and apparently Elgon in its present form. Volcanic activity is not yet at an end, as is evidenced by the many steam-vents and hot-springs in the Rift valley, and the eruption of Teleki's volcano (at the south end of Lake Rudolf) at the close of the 19th century. The breaching of the crater wall of Elgon probably let loose the lava bed which covers the Uasin Gishu plateau. On its sides gneiss and granite are exposed. The surface soil in the highland zone is mainly red clay (in the forested areas) or black-cotton. In the central parts of the Rift valley yellow loam is found. The fourth geological zone, the Lake Victoria belt is in parts covered by lava flows, but the gneiss reappears with granite hills and sedimentary rocks. The Kisii highlands are composed of hard sandstone resembling the Waterberg (Transvaal) series.