WENLOCK SERIES. 95 



Alrypa reiictiJaris, Chonctcs lata, RhvnchoneUa navicula, OrtJiis clfgan- 

 iula, Strophomc7ia depressa, Cardiola interrupta, and Orthoceras 

 primcBviim. 



The Denbigh grits are exposed on the top of Ffriddfawr. The 

 entire series is estimated to have a thickness of about 4000 feet. 

 The Penyglog Grits of Corwen and the Austwick Grits of York- 

 shire belong to the same series.^ In the Dee Valley Mr. J. E. 

 Marr notes the following succession : — 



Lake District. 

 T> K" I1 Vi' (3- Dinas-Bran Beds = Upper Coldvvell Beds. 



Fla^s ^''^ "• Penyglog Grits = Middle and Lower Coldwell Beds. 



*= ■ ( I. Penyglog Flags = Brathay Flags. 



In (i) the Flags or banded slates of Penyglog quarry and 

 Maeshir, Monograptus priodon, Retiolites Geinitziatms, Cyrtograptus 

 Mivxhisoni, and Orthoceras have been obtained. The gritty beds 

 (2) are seen above Penyglog quarry. The highest beds (3) are 

 exposed on the hill near Llangollen, upon which Dinas-Bran Castle 

 stands. They have been correlated with the Llansannan Shales by 

 the Geological Survey. They contain Favosites fibrosus, Rhynchonella 

 navicula, CuciiUella coarctata, Orthoceras tenuicinctinn, etc.^ 



The Penyglog Flags are probably on the same horizon as the 

 Pencerrig beds of Builth, which contain Cyrtograptus Murchisoni. 



At Rhymney quarry near Cardiff there are about 70 feet of 

 sandstones (Rhymney Grit), containing a bed with Ctenodonta 

 subcvqnalis (^Ctetiodonta-SRndstone). These beds are described by 

 Prof. W. J. SoUas as belonging to the Lower Wenlock Beds.^ 



WOOLHOPE BEDS. 



The term Woolhope Beds was given by Murchison from the 

 occurrence of these strata at Woolhope, near Hereford. 



The Woolhope Limestone is regarded as forming a subordinate 

 part of the Wenlock formation, and has been termed the Lower 

 Wenlock Limestone. This formation, which rests on the 

 Tarannon Shales and Upper Llandovery rocks, as seen in Shrop- 

 shire and parts of North Wales, consists of dark grey shale, with 

 subordinate and thin nodular masses of limestone and calcareous 

 sandstone. The formation is rich in Trilobites, Brachiopoda, and 

 also in Cephalopoda : these include Homalonotus delphinocephaliis, 

 Encrinurus punctatus, Acidaspis Brightii, IllcEnus Barrie^isis, Phacops 

 caitdaiiis, Spirifera elevata, S. plicatella, Orthis elegantula, Stro- 

 phonuna euglypha, Leptcena transversalis, Atrypa reticularis, 



1 Hughes, Q. J. XXXV. 694. 



^ Q. J. xxxvi. 283. See also Marr, Cambrian and Silurian Rocks, p. 41. 



3 Q. J. XXXV. 488. 



