IIO PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Arenig Species, St. David's (continued). 



fepecies. 



.Lower. 



Miclclle. 



Upper. 



Brought forward 







11 







18 







22 



Braciiiopoda. 





















# 











* 



























> S P- •; 







* 

















Gasteropoda. 











... 





* 



Pleurotomaria llanvirnensis, Hicks 









Pteropoda. 











* 













* 











Harknessii, Hicks 





* 





Heteropoda. 









Belleroplion fflultistriatus Suit 

















Cephalopoda. 

















caereesiense, Hicks 







* 



Annelida. 















* 





16 



24 



33 



The intimate stratigraphical conformity at St. David's between 

 the Tremadoc and Arenig rocks, and between the latter and the 

 overlying Llandeilo series, is clear and determined, both on the 

 mainland and on Ramsey Island, where both the Tremadoc and the 

 Arenig occupy a considerable area. Much of the centre of the 

 island is composed of the Arenig series, and is prolific in fossils. The 

 slates of St. David's are black and probably of deep-sea origin. The 

 subdivision here by Dr. Hicks into Lower, Middle, and Upper is 

 based upon the distribution of the organic remains and the relation 

 to the Llandeilo above. This comparison is important in its bear- 

 ing upon the value and meaning of the terms Arenig and Lower 

 Llandeilo as applied to at least four areas and groups of rocks in 

 England and Wales, viz. : — Westmoreland, or the Skiddaw group ; 

 Shropshire, or the Stiperstones series ; North Wales, or the Tremadoc 

 and Lfestiniog areas ; and South Wales, or the St.-David's beds. 

 Formerly the Geological Survey regarded three of the groups in the 

 areas above mentioned as belonging to rocks termed Lower Llan- 

 deilo by SirR. Murchison; they were mapped as Llandeilo simply, 



