[ 133 ] 

 XXI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xxxi. p. 441.] 



March 11, 1891.— Dr. A. Geikie, F.R.S., President, in the Chair 



npHE following communications were read : — 



-*- 1. " Manod and the Moelwyns." By A. Y. Jennings, Esq., 



F.L.S., P.G.S., and G. J. Williams, Esq., E.G.S. 



The area described by the authors is on the IS. side of the 

 Merionethshire anticlinal of Lower-Cambrian rocks, and contains 

 Lingula Flags, Tremadoc and Arenig rocks. The authors correct 

 what they think is an inaccuracy of some importance in the correla- 

 tion of beds in different parts of the range, as interpreted in the map 

 and memoir of the Geological Survey, and trace with greater com- 

 pleteness the position and constancy of the beds of slate in the Arenig 

 series — a point of considerable local and practical importance to those 

 engaged in slate-quarrying. They offer also what seems to them to 

 be conclusive evidence to show the intrusive nature of the great crys- 

 talline mass known as the syenite of Tan-y-Grisiau, and to its intrusion 

 are due, in their opinion, the peculiar physical characteristics of the 

 surrounding country. Though in the immediate neighbourhood of 

 Festiniog there is no direct evidence of unconformity between the 

 Tremadoc and Arenig series, it seems probable that an unconformity 

 does exist ; for when traced toward the west the Tremadoc beds thin 

 out and the Lingula Plags are overlain by graptolite-bearing slates of 

 Arenig age, while eastward, near Llyn Serw, the grit comes close upon 

 Upper-Lingula Flags. The division of the Arenig volcanic rocks into 

 Lower Ashes, Felstone, and Upper Ashes, while true of some districts 

 and useful as a generalization, conveys an idea of uniformity of strata 

 all round the Anticlinal which more detailed examination of different 

 districts does not support. 



2. "The Tudor Specimen of Eozoon." By J. W. Gregory, Esq., 

 F.G.S., F.Z.S. 



March 25.— Dr. A. Geikie, F.R.S., President, in the Chair. 

 The following communications were read : — 



1. " Notes on Nautili and Ammonites." By S. S. Buckman, 



Esq., P.G.S. 



2. « On the Drifts of Plamborough Head." By G. "W. Lamplugh, 

 Esq., P.G.S. 



The author describes in detail the characters and distribution of 

 the glacial deposits on Plamborough Head, and classifies them as 

 follows : — 



Alluvial wash, freshwater marls, &c B,ecent. 



Late glacial gravels "] 



Upper Boulder Clay | 



Intermediate Series. Stratified beds with bands of ! p, • i 



Boulder Clay j a a ' 



Bnsement Boulder Clay j 



Chalky rubble J 



" Infra-glacial" beds of Sewerby and Speeton. 



