CHAPTER II 



DERIVATION OF THE FAUNA, GEOGRAPHICALLY 

 AND PALEONTOLOGICALLY 



A — Geologic Formation 



The greater part of the area comprised in British East 

 Africa and Uganda is of Archaean age, being gneissic in 

 structure and derivation. All of the desert lowlands and 

 the higher grass-lands which flank them are comprised in 

 the gneissic area, together with the hills and mountains 

 which rise above them, including the lofty fault range of 

 Ruwenzori. Capping the central portion of the Archaean 

 region we find a more recent volcanic or eruptive rock 

 series composed of various lavas. The whole highland 

 region of both East Africa and Uganda, including the lofty 

 volcanoes of Kenia, Elgon, and Kilimanjaro, are of this 

 formation. The Rift Valley has been the most recent 

 source of the lava cap which covers the highlands. The 

 lavas of this age have been erupted from fissures in the 

 vicinity of the Rift Valley, which comparatively recently 

 formed a great arch of eruptive rock, from the apex of 

 which the lava flowed east and west over the gneissic 

 region. Later the central portion of the arch dropped a 

 few thousand feet, forming the great rift, now known as 

 the Rift Valley. Muff in his account of the geology of 

 British East Africa * has described this formation as the 



* Colonial Reports, Misc., No. 45, Jan., 1908, p. 27. 

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