These rocks prevail in the districts of Taru, Nandi and throughout Ukamba. A course gneiss is the predominant rock, but is associated with garnetiferous mica-schists and much intrusive granite. Hornblende schists and beds of metamorphic limestone are rare. Cherty quartzites interbedded with mylonites occur on the flanks of the Nandi hills, but their age is not known.
The grits of Masara, near Rabai mission station and Mombasa, have yielded specimens of Glossopteris browniana var. indica, thus indicating their Karroo age.
Shales and limestones of this age are well seen along the railway near Changamwe. They contain gigantic ammonites. According to Dr Waagen the ammonites show a striking analogy to forms from the Acanthicus zone of East India. Belemnites are plentiful.
These are feebly represented by some boulder beds on the higher slopes of Kilimanjaro and Kenya. They show that in Pleistocene times the glaciers of Kilimanjaro and Kenya extended much farther down the mountain slopes.
The ancient and more modern lake deposits have so far yielded no mammalian or other organic remains of interest.
A belt of volcanic rocks, over 150,000 sq. m. in area, extends from beyond the southern to beyond the northern territorial limits. They belong to an older and a newer set. The older group commenced with a series of fissure eruptions along the site of the present rift-valley and parallel with it. From these fissures immense and repeated flows of lava spread over the Kapte and Laikipia plateaus. At about the same time, or a little later, Kenya and Kimawenzi, Elgon and Chibcharagnani were in eruption. The age of these volcanic outbursts cannot be more definitely stated than that they are post-Jurassic, and probably extended through Cretaceous into early Tertiary times. This great volcanic period was followed by the eruptions of Kibo and some of the larger volcanoes of the rift-valley. The flows from Kibo include nepheline and leucite basanite lavas rich in soda felspars. They bear a close resemblance to the Norwegian "Rhombenporphyrs." The chain of volcanic cones along the northern lower slopes of Kilimanjaro, those of the Kyulu mountains, Donyo Longonot and numerous craters in the rift-valley region, are of a slightly more recent date. A few of the volcanoes in the latter region have only recently become extinct; a few may be only dormant.
Donyo Buru still emits small quantities of steam, while Mount Teleki, in the neighbourhood of Lake Rudolf, was in eruption at the close of the 19th century.]
In its climate and vegetation British East Africa again shows an arrangement of zones parallel to the coast. The coast region is hot but is generally more healthy than the coast lands of other tropical countries, this being due to the constant breeze from the Indian Ocean and to the dryness of the soil. The rainfall on the coast is about 35 in. a year, the temperature tropical. The succeeding plains and the outer plateaus are more arid. Farther inland the highlands - in which term may be included all districts over 5000 ft. high - are very healthy, fever being almost unknown. The average temperature is about 66° F. in the cool season and 73° F. in the hot season. Over 7000 ft. the climate becomes distinctly colder and frosts are experienced. The average rainfall in the highlands is between 40 and 50 in. The country bordering Victoria Nyanza is typically tropical; the rainfall exceeds 60 in. in the year, and this region is quite unsuitable to Europeans. The hottest period throughout the protectorate is December to April, the coolest, July to September. The "greater rains" fall from March to June, the "smaller rains" in November and December. The rainfall is not, however, as regular as is usual in countries within the tropics, and severe droughts are occasionally experienced.
In the districts bordering Victoria Nyanza the flora resembles that of Uganda (q.v.). The characteristic trees of the coast regions are the mangrove and coco-nut palm. Ebony grows in the scrub-jungle. Vast forests of olives and junipers are found on the Mau escarpment; the cotton, fig and bamboo on the Kikuyu escarpment; and in several regions are dense forests of great trees whose lowest branches are 50 ft. from the ground. Two varieties of the valuable rubber-vine, Landolphia florida and Landolphia Kirkii, are found near the coast and in the forests. The higher mountains preserve distinct species, the surviving remnants of the flora of a cooler period.
The fauna is not abundant except in large mammals, which are very numerous on the drier steppes. They include the camel (confined to the arid northern regions), elephant (more and more restricted to unfrequented districts), rhinoceros, buffalo, many kinds of antelope, zebra, giraffe, hippopotamus, lion and other carnivora, and numerous monkeys. In many parts the rhinoceros is particularly abundant and dangerous. Crocodiles are common in the larger rivers and in Victoria Nyanza. Snakes are somewhat rare, the most dangerous being the puff-adder. Centipedes and scorpions, as well as mosquitoes and other insects, are also less common than in most tropical countries. In some districts bees are exceedingly numerous. The birds include the ostrich, stork, bustard and secretary-bird among the larger varieties, the guinea fowl, various kinds of spur fowl, and the lesser bustard, the wild pigeon, weaver and hornbill. By the banks of lakes and rivers are to be seen thousands of cranes, pelicans and flamingoes.