﻿578 DEi T. GEOOit A^'D MR. p. LAKE ox THE [XoV. I908, 



(9) Pron-Er^'s Slates. — "Wherever the beds immediately above 

 the Glyn Grit are exposed, they consist of grey slates with thin 

 arenaceous bauds, and are similar in character to those that we 

 have already described at Corwen. Occasionally they contain 

 darker bands, but nowhere in this district have we discovered any 

 graptolites such as are found at Corwen. As at Corwen, the slates 

 show peculiar dark ramifications which easily distinguish them from 

 any other beds with which we are acquainted. On the western 

 side of Fron Frys they are some 50 feet thick. 



These slates may be traced, following the Corwen Grit on its 

 north side, wherever the latter is to be seen. The best exposures 

 are perhaps in the stream at Tomen-y-meirw ; on the northern 

 slopes of Cefn-coch ; in the valley of Xant Llafar ; and on the 

 hill of Fron Frys. In the eastern part of the map (PI. LIII) 

 they are also visible at one or two places. 



There is a large quarry in these beds, close to the road 

 near Hafod-y-gynfawr, in which the rock is considerably darker 

 than is usual elsewhere ; but this is probably due to the fresh- 

 ness of the exposed surfaces. No fossils were obtained in this 

 quarry. 



At Corwen we found very few fossils in these beds, with the 

 exception of the graptolites in the black bands. But on Mynydd 

 Fron Frys and Cefn-coch fossils are fairly abundant, and show 

 clearly that the slates belong to the Llandovery Series. Brachiopods 

 are the most abundant forms, and the most characteristic are 

 Pentamerus undatus and several species of Meristina. Among the 

 corals may be mentioned Nididites favus. 



•a|' 

 |2 



List of Fossils from the Peox-Frys Slates. 



•Si 



-1 





ll 



X 



Lindstroemia subduplicata (?) 



Orthis Acto7ii(B, Sow 



X 



X 



M'Coy. 

 Petraia elongata (1) Phil. 



Orthis hiloha, Linn 



X 

 X 



\. Orthis calligramma, Dalm. (c) ... 



X 



Monticulipora fibrosa, Goldf. 

 (c). 



Orthis crispa, M'Coy 



X 





Orthis elegantida, Dalm. (c) 



X 





NiduUtes favus, Salt. (c). 



Orthis hirnantensis (?) M'Coy , . . 

 Orthis plicata, Sow. 



X 





Atrypa marginalis, Dalm. (c). 

 Leptella (?) cf. Uandeileensis, 



Orthis pm'cat a, M'Coy 



X 



X 



Pentamerus undatus, Sow. (c). 







Dav. 



Tlatystrophia hiforata, Schl 



X 



X 



Leptfsna quinquecostata, M'Coy 



Fleet arahonites sericea (?) Sow. ... 



X 





(c). 



Bafinesqidna expansa (?) Sow. ... 



X 



X 



LeptcBua rhomhoidalis, Wilck. 

 Meristina (?) cf . crassa, Sow. 



Triplesia cf. insularis, Eichw. ... 



X 





Meristina (?) cf. furcata, Sow, 



Acidaspis sp. 







Meristina (?) sp. (c). 



Encrinuruspunctatus, Brongn. 







Meristina (?) sp. 



Illcsmts sp. 





