332 



Geological Society 



slight for their purpose ; if so, the book is not intended for them, 

 but for those only who, while wishing to gain a general idea of 

 the important work done during the last dozen years, find the 

 more authoritative popular accounts too advanced for them. 



XXXIV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 208.] 



May 12th, 1909,— Prof. W. J. Sollas, LL.D., ScD., F.R.S., President, 



and afterwards Dr. J. J. H. Teall, M.A., F.R.S., Vice-President, 



in the Chair. 



rPHE following communications were read : — 



1. ' The Hartfell-Valentian Succession around Plynlimon and 

 Pont Erwyd (North Cardiganshire).' By Owen Thomas Jones, 

 M.A., B.Sc, E.G.S. 



In this paper the author deals with the stratigraphical suc- 

 cession and the geological structure of an area of about 40 square 

 miles, lying in the hilly district about 12 to 16 miles east of 

 Aberystwyth. In an historical introduction the work of previous 

 observers, including Sedgwick, llamsay, and Walter Keeping, is 

 dealt with. 



The rocks within the district arc divided into three Stages, which 

 are further subdivided into Groups and Zones, as follows : — 



YSTWYTH 



Stage. 



(c) Rhuddnant C 2 

 Group. (1 



(b) My her in 



Group. 



2. Rhuddnant Grits. 

 Rhuddnant Shales. 

 Blaen Myherin Mudstones. 

 Dohven Mudstones. 



it 



Post 

 Ekwyd 



Stage. 



(a) Devil's Bridge ), T , , ... ,. . ., , , 



Group ? Mudstones with thin grit-bands. 



P 



I 



1 



(c) Castell 



G r o it p 



<{ (b) Rheidol 

 G r o u p 



(a) Eisteddfa 

 Group. 



f3. Flags and shales. (Zone of MonograpUis sedgwicli .) 

 2. Shales and mudstones. (Zone of CepJ/alograptvs 



cometa.) 

 L. Mudstones and shales. (Zone of Monograph's 



convohitv.s.) 



f~4. Blaelc shales and mud- f d. LeptotJieca-band. 

 stones. j y. Magnus-hand. 



(Zone of 3fonograptus \ j3. Triangulatns-haud. 

 communis.) \^ a . Triangulatus-xav. band. 



^ 3. Flags and black shales. (Zone of Monograptus 



cyphus, s. s.) 

 2. Flags with thin shales. (Zone of Monograptus 



sp. nov.) 

 ^1. Flags and shales. (Zone of Monograptus sp. nov.) 

 ("2. Flags, shales, and grits. (Zone of Cephalograptns 



? acumhiatus.) 



1. Flags with thin shales. 



(Zone of Glyptograptvs 

 L t_ -perseulpfvs.) 



f (e) Brynglas Group. Mudstones. 



PiiYNLiMOx] (b) Drosgol Group. Grits, conglomerates, and mudstones. 



stage. j ^ Nant-y-raoch Flags with thin shales. (Zone of Dieellograptus 



y_ Group. anceps.) 



