﻿592 



DR. 



T. GROOil AND MR. P. LAKE 0>J THE [-^OV. I908, 



It has already been noted that the Glyn Grit is merely a sandy 

 and calcareous facies of the upper part of the Dolhir Beds ; and 

 the general results of our comparison of the Bala Series of these 

 areas may, therefore, be summarized in the following; table. As 

 the faunas of the various subdivisions of the Ashgillian Series are 

 still very imperfectly known, no attempt is made in this table to 

 correlate these subdivisions : — 





South Wales. 



1 

 Glyn Ceiriog. 



Lake District. 



Ashgillian. 



fSlade Beds. 



EedMll Beds. 



^ Sholeshook Limestone. 



Robeston-Wathen Lime- 

 L_ stone. 



r 



Glyn Grit. 

 ^ Dolhir Beds. 



I 



Fhyllopora-Bedis. 



^ Ashgill Shales. 



1 



Staurocej)hahis-Jjime- 

 (^ stone. 



Caeadocian. 



— Gap? — 

 Dicranoc/raptits-Shales. 



Graptolitic Slates. 

 — Gap. — 

 Bryn Beds. | 

 Teirw Beds. 



Sleddale Beds. 

 Roman-Fell Group. 



The Fron-Prys Slates differ so much from those of the Lake 

 District, and so little is known of the corresponding beds in South 

 Wales, that direct comparison with those areas is impossible. 

 Instead of graptolites they contain brachiopods and corals, and thus 

 belong to the shelly facies of the Llandovery which prevails on 

 the eastern borders of Wales. They are, however, continuous and 

 lithologically identical with the Grey Slates of Corwen, in which we 

 found graptolitic bands containing graptolites of the Monograptus- 

 gregarius Zone. This is the uppermost zone of the Lower Birkhill 

 Shales of Moffat, and it is therefore with the Lower Birkhill that 

 the Grey Slates of Corwen and the Lron-Frys Slates of Glyn 

 Ceiriog must be correlated. At Glyn w^e have found no graptolites, 

 but the slates contain Pentamerus undatus, Meristina (?) cf. crassa, 

 several other species of Meristina, and Nidulites javus. It is clear 

 therefore that they belong to the Llandovery of the original Silurian 

 area, and probably to the lower division of that series. It is 

 interesting to note that, while the shelly facies of the Llandovery 

 is found at Glyn, graptolitic bands have already made an aj)pearance 

 at Corwen, which lies only 8 miles away to the west. Parther west 

 graptolites become still more abundant in the corresponding beds. 



With the exception of the Tarannon graptolite MonograptusMarri. 

 no fossils have yet been found at Glyn Ceiriog between the Fron-Prys 

 Slates and the Wenlock Beds ; but the former appear to pass without 

 a break into the pale-coloured Tj^-draw Slates, and these in turn to 

 graduate upwards into the slates of the Wenlock Series. It seems, 

 therefore, that the Ty-draw Slates must represent both the Upper 



