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Archaean
10. Schists and quartzites of Nandi.
11. Gneisses, schists, granites.
Igneous and Volcanic.
Recent
Active, dormant and extinct volcanoes.
Post-Jurassic to Pleistocene
Kibo and volcanoes of the rift-valley.
Kimawenzi, Kenya and plateau eruptions.
Archaean.?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.
Carboniferous??From shales on the Sabaki river Dr Gregory obtained fish-scales and specimens of Palaeanodonta Fischeri.
Karroo.?The grits of Masara, near Rabai mission station and Mombasa, have yielded specimens of Glossopteris browniana var. indica, thus indicating their Karroo age.
Jurassic.?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.
Pleistocene.?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.
Recent.?The ancient and more modern lake deposits have so far yielded no mammalian or other organic remains of interest.
Igneous and Volcanic.?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.]
