[ 490 ] 

 XL VIII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 416.] 



January 24th, 1900.— W. Whitaker, B.A., F.R.S., President, 

 in the Chair. 

 T^HE following communications were read : — 

 -*- 1. 'Fossils in the University Museum, Oxford: II. — On Two 

 New Genera and Species of Crinoidea.' By W. J. Sollas, M.A., 

 D.Sc, LL.D., F.R.S., V.P.G.S., Professor of Geology in the University 

 of Oxford. 



2. ' Fossils in the University Museum, Oxford : III. — A JNew 

 Worm-track from the Slates of Bray Head, Ireland, with Observa- 

 tions on the Genus Oldhamia.' By \V. J. Sollas, M.A., D.Sc, LL.D., 

 F.R.S., Y.P.G.S., Professor of Geology in the University of Oxford. 



3. ' Contributions to the Geology of British East Africa : Part II. 

 —The Geology of Mount Kenya.' By J. W. Gregory, D.Sc, F.G.S. 



The three main zones of Kenya are characterized by different 

 geological features. The long slope of the forest-belt consists in 

 the main of volcanic ash, though the remains of secondary parasitic 

 craters occur in it. The Alpine zone consists of coarser ash, 

 agglomerates, and tuffs, interbedded with lava-flows and traversed 

 by numerous dykes, with the remains of some secondary centres 

 of eruption. The third zone, or central peak, consists of the plug 

 which choked the central vent, of beds of agglomerate, and the thick 

 proximal ends of the great lava-flows. 



The rocks of the central core comprise an olivine-anorthoclase- 

 nepheline- syenite with segyrine, and a black glassy lava with 

 numerous white phenocrysts of anorthoclase ; this rock is allied in 

 some respects to the pantellerites, but receives a special name both 

 here and in its occurrence in lava-flows. 



The dyke-rocks fall into two categories — a series of phonolites, 

 and one of basalts and dolerites. One, at least, of the dykes is 

 compound, including both these rock-types. The basic group ranges 

 from basalts with little olivine to coarsely crystalline dolerite rich 

 in that mineral. 



The lavas belong to three main groups: — (1) Those of the 

 nepheline-syenito series, (2) the phonolites, and (3) the basalts. 

 The oldest lavas appear to be the phonolites, but they and the 

 first group of lavas seem to have overlapped in age ; the olivine- 

 basalts, which reach the surface from a zone of secondary craters 

 in the Alpine zone, are the latest in date. The first group of 

 lavas are rhyolitic in aspect, and consist of a brown or green 

 glass in which are embedded phenocrysts of anorthoclase, and 

 green needles which show the optical characters of segyrine. As 

 these rocks do not conform to Bosenbusch's definition of pantel- 

 lerites, a new name is proposed for them ; the author considers 

 that the pantellerites may be liparitic equivalents of the dacites, 

 whilo these Kenya rocks correspond with the nephelme-syenites. 



