[ 384 ] 

 XLIV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 152.] 



December 9, 1891.— Sir Archibald Geikie, D.Sc, LL.D., F.R.S., 



President, in the Chair. 



HPHE following communications were read : — 

 -*- 1. " On the Hocks mapped as Cambrian in Caernarvon- 

 shire." By the Rev. J. F. Blake, M.A., F.G.S. 



In this paper the following is given as a definite succession in the 

 Cambrian series: — 1. Pale Slates; 2. Upper Purple Slates; 3. St. 

 Aun's Grit ; 4. Lower Purple Slates ; 5. Rhiw-wn Grit ; 6. Hard 

 banded Pale Slates and Halleflintas ; 7. Bangor Conglomerate ; 

 8. Hard banded Pale Slates and Halleflintas ; 9. Bangor Breccia ; 

 10. Blue banded laminated Grits; 11. TairfTynnon Conglomerate; 

 12. Blue banded laminated Grits ; 13. Brithdir quartz-felsite Grit. 



The general succession is argued to be the same in the isolated 

 portion east and south of Bangor as in the main mass. The existence 

 or otherwise of a base on the mainland is considered to depend on 

 the age assigned to the Dinorwic felsite, and the presence of the 

 summit-beds to depend on whether the Bronllwyd Grit (stated to 

 belong to the overlying group) rests conformably or unconformably 

 on the Cambrian rocks. 



It is argued that the rocks to the west of the Llyn Padarn felsite 

 belong to the lower part of the series and those to the east to the 

 upper, and that the felsite is a volcanic complex belonging to the 

 middle of the Cambrian period. 



A post-Cambrian age is assigned to the conglomerates of Moel 

 Tryfan and Llyn Padarn, thus causing the break at the base of the 

 Silurian system to assume an increased importance. 



2. " The Subterranean Denudation of the Glacial Drift, a probable 

 cause of submerged Peat and Forest-beds." By W. Shone, Esq., 

 F.G.S. 



A description is given of a section at Upton, Chester, where 

 Boulder Clay rests upon a mid-glacial sands." The Boulder Clay 

 sinks to a lower level in the small valleys which are cut through 

 into the sands ; and the author supposes that this is due to the 

 subterranean denudation of the sands, which would be greatest near 

 the valleys, and become less at a distance from them. He con- 

 siders such denudation is capable of producing submerged peat and 

 forest-beds, and accounts for the splitting of peat-beds, as described 

 by Mr. G. H. llorton, by a somewhat similar action, which he 

 believes may have also operated in Carboniferous times, causing the 

 splitting of coal-seams. 



