OBITS OF CORWEN, NORTH WALES. 211 



like those in the valley south of Llansantfrraid, on the road to 

 Llanarmon. 



Along the strike of the Llansantflraid mudstones toward the S.E. 

 we find a curious bed, indicated by a blue line in the Survey Map. 

 This consists of alternations of bands of Limestone and fine Sandstone 

 with wavy lines, very like that into which the Corwen Grit passed 

 in several places. In this I saw several traces of fossils. The only 

 ones I was able to make out were Favosites alveolaris and a large 

 form of Orthis calligramma. 



Both the Limestone and the tramway mudstone pass under the 

 Pale Slates ; and these are overlain by the Denbigh Flags, which are 

 worked in the large quarries near Llansantflraid. A bed of Sand- 

 stone seen on the hillside north of the village may represent the 

 Grit of Penyglog, near Corwen. 



The points that seem to me clear are : — that the Corwen Grits 

 are distinct from the Penyglog Grits ; that there is more evidence of 

 a discordancy at their base than at the base of the Pale Slates or of 

 the Penyglog Grits ; that there are generally some beds of con- 

 glomerate, sandstone, or limestone with sandstone on the horizon of 

 the Corwen Grits ; that the general facies of the few fossils obtained 

 from these beds in the district examined is that of the May-Hill 

 rocks ; that the mudstones of the ravine north of Plasuchaf are the 

 same as those of the tramway-cutting south-west of Llansantflraid. 



Other questions remain to be worked out. Are these mudstones 

 (which have not yet been found immediately underlying the Corwen 

 Grits) merely a local development of those Grits ? or are they a lower 

 part of the same group locally developed to a greater thickness ? or 

 are they a higher part of the underlying Bala series here and there 

 overlapped by the Silurian Rocks ? 



I have thought it better to bring forward what I have done, and 

 invite cooperation along the same line of investigation, rather than 

 to wait till I could offer more definite results. 



Discussion. 



Prof. Kamsay said that about Builth and all round the Longmynd 

 area, and, indeed, over a great part of South Wales, we find Cam- 

 brian and Lower Silurian rocks overlain unconformably by the 

 Pentamerus-limestone or Upper Llandovery rocks, upon which, 

 north of the Builth country, and also in part of South Wales, 

 come the Tarannon shales and the Denbigh grits with Wenlock 

 fossils, overlain again by the ordinary Wenlock shales. He was 

 particularly pleased, therefore, to hear that Pentamerus oblongus 

 occurred in the beds where Prof. Hughes said it was present, as this 

 was strongly in favour of his own opinion that the Upper Silurian 

 strata were transgressive in the Corwen district. 



Mr. Hicks considered the Lower (or Corwen) Grits to be the 

 equivalents of the grits at the base of the Lower Llandovery rocks 

 in South Wales. The Upper (or Penyglog) Grits are nearer to the 

 horizon of the May-Hill Sandstones. There was no visible un- 



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