138 Geological Society : — 



concerning the discharge of Tanganyika by the Lukuja. It is 

 suggested that the rise of the lake is due to the blocking-up of the 

 river by vegetation, assisted by silting during the first rains, whilst 

 the fall is produced by the destruction of the barrier formed in this 

 manner. 



May 11.— W. H. Hudleston, Esq., M.A., F.B.S., 

 President, in the Chair. 

 The following communications were read : — 



1. " On the so-called Gneiss of Carboniferous age at Guttannen 

 (Canton Berne, Switzerland)." Bv Prof. T. G. Bonney, D.Sc, 

 LL.D., F.R.S., V.P.G.S. 



It is stated by Dr. Heim (Quarterly Journal, vol. xlvi. p. 237) 

 that the stems of Galamites have been found at Guttannen in a 

 variety of gneiss, i. e. in one of a group of rocks which exactly 

 " resemble true crystalline schists in mode of occurrence. Petro- 

 graphically they are related to them by passage rocks ; at least the 

 line of separation is not easily distinguished. . . .The Palaeozoic 

 formations mostly show an intimate tectonic relation to the crystal- 

 line schists, and have been converted petrographically into crystal- 

 line schists." 



The author describes the result of a visit to the section at Gut- 

 tannen in company with Mr. J. Eccles, F.G.S. (to whom he is 

 greatly indebted for kind assistance), and of his subsequent study of 

 the specimens then collected. The belt of sericitic " phyllites and 

 gneisses," presumably of Carboniferous age, represented on the Swiss 

 geological map (Blatt xiii.) as infolded, at and above Guttannen, in 

 true crystalline gneissoid rocks, is found on examination to consist 

 partly of true gneisses, partly of detrital rocks. The boulder from 

 which the stems in the Berne Museum were obtained belongs to the 

 latter. These rocks sometimes present macroscopically, and occa- 

 sionally even microscopically, considerable resemblance to true 

 gneisses, but this proves on careful examination to be illusory. 

 They are, like the Torridon Sandstone of Scotland, or the Gres 

 feldspathique of Normandy, composed of the detritus of granitoid or 

 gneissoid rock, which sometimes forms a mosaic resembling the 

 original rock, and which has been generally more or less affected by 

 subsequent pressure and the usual secondary mineral changes. Thus, 

 if the term be employed in the ordinary sense, they are no more 

 gneisses than the rocks of Carboniferous age at Vernayaz (Canton 

 Valais) are micaschists, but in some cases the imitation is unusually 

 good, and, so far as the author saw, there are at Guttannen neither 

 conglomerates nor slates to betray the imposition, as happens at the 

 other locality. 



2. " On the Lithophyses in the Obsidian of the Rocche Bosse, 

 Lipari." By Prof. Grenville A. J. Cole, F.G.S., and Gerard 

 W. Butler, Esq., B.A., E.G.S. 



The rock described in this paper differs in no essential particular 

 from that at Forgia Yecchia, or from the obsidian on the north flank 



