PROOEEDliYGS 



THE GEOLOGICAL SOCIETY OF LONDON. 



Vol. IV. Part IL 1843—1844. No. 99. 



November 29, 1843. 



Joseph Travis Clay, Esq., and Francis W. Jennings, Esq., 

 were elected Fellows of this Society. 



The following communication, a part of which had been read at 

 the previous meeting, was concluded : — 



On the Oldek Palaeozoic (Protozoic) Rocks of North Wales. 

 By the Rev. A. Hedgwjck, M.A., F.R.8., Woodwardian Pro- 

 fessor of Geology and Fellow of Trinity College in the Univer- 

 sity of Cambridge. 



§ 1. Introduction^ 



In a paper i^ead before the Geological Society in June, 1843, 

 and intituled, " An Outline of the Geological Structure of North 

 Wales,"* the author gave a descri[)tion of those stratified rocks 

 in the northern counties of the principality which arc of anterior 

 date to t})e mountain limestone. Those rocks he separated into 

 the following three principal groups : — 



1. Chlorite-slate and mica-slate. These form a band along the 

 north-western side of the promontory of Carnarvonshire from Forth 

 Dilleyn to Bardsea island. 



2. Greywacke and roofing slate, often containing calcareous 

 bands, and alternating with Plutonic rocks of cotemporaneous 

 formation : and these rocks the author terms, in his present paper, 

 the Protozoic, group. They extend in an east and west direction, 

 from the borders of Shropshire to the western coast of Carnarvon- 

 shire ; and their north-western boundary, from the confines of 

 Shropshire to Yspytty Evan, coincides nearly with the Holyhead 

 road ; and from Yspytty Evan to Conway, with the Conway river. 



3. An overlying and sometimes unconformable deposit of flag- 



* Proceedings of the Geological Society, vol. iv. p. 212. 

 VOL. l^•. PART II. U 



