Vol. 56.] THE GEOLOGY OF MOUNT KENYA. 205 



10. Contributions to the Geology of British East Africa. — Part II. 1 

 The Geology of Mount Kenya. By Prof. J. W. Gregory, 

 D.Sc, F.G.S. (Eead January 24th, 1900.) 



[Plates X, XI, & XII (pars).] 



Contents. 



Page 



I. Introduction 205 



II. Physical Geography of Mount Kenya 207 



III. Petrography 207 



1. The Rocks of the Central Core 208 



2. The Dyke-rocks 210 



(a) The Phonolites. 

 (&) The Basic Dykes. 



3. The Lavas 211 



(a) The Kenytes. 



(b) The Phoaolites. 



(c) The Basalts. 



4. The Pyroclastic Eocks 216 



IV. The Stratigraphy of Mount Kenya 216 



V. The Geological History of Mount Kenya 218 



VI. Kenya and Kiliraa Njaro 220 



VII. Summary of Conclusions 221 



I. Introduction. 



Mount Kenya, the greatest mountain in British East Africa, was 

 discovered by Ludwig Krapf, 2 when on December 3rd, 1849, 

 he saw its two-horned summit from a hill above the Wakamba 

 village of Kitui. No suggestion as to the structure of Kenya was 

 made until 1883, when Joseph Thomson, after a view of the 

 mountain across the Laikipia plateau, described it as the denuded 

 remnant of an old volcano. ' The peak/ he tells us, 3 ' without a 

 doubt represents the column of lava which closed the volcanic life 

 of the mountain .... The crater has been gradually washed away/ 

 The first definite geological information about Kenya we owe to 

 Count S. Teleki, who was the first European to reach the mountain ; 

 in 1887 he climbed the western slopes to the height of about 

 13,800 feet, and brought back some rock-specimens which have 

 been described in detail in a valuable memoir by A. Rosiwal. 4 This 

 petrologist determined the specimens as augite-andesite, andesite- 

 pitchstone (hyalo-andesite), and phonolite, and thus proved the 

 volcanic nature of the mountain. 



1 Part I, ' The Glacial Geology of Mount Kenya,' was published in this 

 Journal, vol. 1 (1894) pp. 515-530, with maps, etc. 



2 ' Travels, Researches, & Missionary Labours ... in Eastern Africa' 1860, 

 p. 544. 



3 ' Through Masai-Land ' 4th ed. (1887) p. 224. 



4 ' Ueber Gesteine aus dem Gebiete zwisehen Usambara u. dem Stefanie-See " 

 Denkschr. d. k. Akad. d. Wissensch. Wien, vol. lviii (1891) pp. 496-498. 



Q. J. G. S. No. 222. q 



