Yol. 56.] GEOLOGY OF MOUNT KENYA. 221 



studied, ranging from Gustav Rose l and J. Roth's 2 descriptions of 

 the collection of von der Decken, and Prof. Bonney's 3 account of 

 the specimens obtained by Sir H. H. Johnston, down to the more 

 recent and detailed descriptions of J. S. Hyland, 4 A. C. Tenne, 5 and 

 A. Rosiwal, 6 but the stratigraphical relations of the rocks are 

 uncertain. Thus, as Baron E. Stromer von Reichenbach 7 has re- 

 marked, ' we are not yet able to decide further as to the character 

 of the rocks of Kilima Njaro, for the positions of its separate points 

 of eruption, its lava-streams, etc., have not yet been systematically 

 investigated.' 



So far as concerns the evidence of the Teleki Valley quadrant, 

 Mount Kenya has had a shorter geological history and is built up 

 of a narrower range of rock-types than Kilima Njaro. The rocks 

 of the latter range from limburgites to obsidians, from peridotites 

 to trachytes. 8 On Mount Kenya I found nothing so basic as a 

 limburgite, or so acid as a trachyte : that mountain probably repre- 

 sents, therefore, only a small part of the long volcanic history of 

 Kilima Njaro. In point of structure Mount Kenya is now in the 

 condition of the Mawenzi peak of Kilima Njaro ; and, according 

 to Mr. Prior, the two peaks probably correspond petrographically, 

 for he finds that rock-specimens from Mawenzi in the Natural 

 History Museum present characters, both macroscopic and micro- 

 scopic, very similar to those of the kenyte-1 



YII. Summary op Conclusions. 



(i) Mount Kenya is an ancient, much-eroded volcano ; the highest 

 peak is formed of the rocks of the central plug ; the site of the 

 crater-walk is marked by the agglomerates, ashes, and tuffs of the 

 Alpine zone. 



(ii) The main lava-series is formed of kenytes, rocks allied to 

 pantellerites, but of a somewhat more basic type. 



(iii) The lowest exposure of the central core is an olivine- 

 bearing nepheline-syenite. 



(iv) The lava-sequence is : firstly, phonolite ; secondly, kenytes ; 

 and finally, olivine-basalts. 



1 ' Beschreibung der von Herrn von der Decken gesandten Gebirgsarten aus 

 Ost-Afrika, grosstentbeils vorn Fusse des Kilimandjaro ' Zeitschr. Allgem. Erdk. 

 Berlin, n. s. vol. xiv (1863) p. 245. 



2 'Beschreibung der zweiten Reihe der von Herrn von der Decken aus der 

 Gegend des Kilimandjaro mitgebrachten Gebirgsarten ' ibid: n. s. vol. xv (I860) 

 pp. 543-45. 



3 ' Report on the Rocks collected by H. H. Johnston from the upper part of 

 the Kilima-Ndjaro Massif Rep. Brit. Assoc. 1885 (Aberdeen) pp. 682-85. 



4 ' Ueber die Gesteine des Kilimandscbaro u. dessen Umgebung ' Tscherm. 

 Min. Petr. Mitth. vol. x (1889) pp. 203-70 & pi. vii. 



5 ' Die Gesteine des Kiliinandscharo-Gebietes ' in H. Meyer's ' Ostafrikaniscbe 

 Gletscherfahrten ' (1890) pp. 305-10; see also Oalder's transl. London 1891, 

 pp. 346-51. 



6 ' Ueber Gesteine aus dem Gebiete zwiscben Usambara u. dem Stefanie-See ' 

 Denkschr. k. Akad. Wissensch. Wien, vol. lviii (1891) pp. 483-87. 



7 ' Geol. deutsch. Schutzgeb. in Afrika ' Munich 1896, p. 55. 



8 F. H. Hatch, ' On a Hornblende-Hypersthene-Peridotite from Losilwa, a 

 low hill in Taveta District, at the S. foot of Kilimandjaro, E. Africa' Geol 

 Mag. 1888, pp. 257-60. 



Q. J. G. S- No. 222. e 



