THE ANCIENT ROCKS OF ST. DAVID'S. 193 



EXPLANATION OF PLATES. 



Plate VIII. 



Map and sections showing the arrangement of the ancient rocks of St. David's. 



Fig. 1. Geological Map of the neighbourhood of St. David's. Scale 1 inch to 

 1 mile. 



2. Section from Point St. John, by St. David's, to a point near Solva 



Harbour. 



3. Section across the N.N.E. end of Ramsey Island. 



4. Section from the valley south of Tygwyn to the cliff north of St. David's 



Head. 



5. Section from Tretio to the coast, on the east side of Aber-pwll in Aber- 



eiddy Bay. 



6. Section from Cwm-wdig to the cliff of Barry Island in a line with the 



Geological-Survey section No. 1, Sheet 1. 



Plate IX. 

 Figs. 1, 2. Placoparia cambriensis, sp. nov. From Llanvirn Quarry : Upper 

 Arenig. 

 3, 4. Pkacops llanvirnensis, sp. nov. Ditto: ditto. 



5. Illcenopsis acuticaudata, sp. nov. Ditto : ditto. 



6. Trinucleus Etheridgei, sp. nov. Ditto : ditto. 



7. llltsnus Hughesii, sp. nov. Ditto : ditto. 



8. Barrandea Homfrayi, sp. nov. Ditto; ditto. 



Plate X. 



Figs. 1, 2. Trinucleus Bamsayi, sp. nov. From Porth-hayog, Ramsey Island. 



3. Mglina obtusicaudata, sp. nov. Llanvirn Quarry : Upper Arenig. 



4, 5. Calymene Hopkinsoni, sp. nov. Ditto : ditto. 



6. Dinobolus ? Hicksii, sp. nov. Ditto : ditto. 



7. Ampyx Salteri, Hicks. Whitesand-Bay Slate Quarry : Middle Arenig. 



8. Ampyx Salteri, Hicks. Ditto : ditto (in Mr. Homfray's collection). 



9. 9a. Mglina Boia, Hicks. Ditto : ditto (in Cambridge Museum). 



10. Agnostus hirundo, Salter. Ditto : ditto (in Cambridge Museum). 



11. Theca Harknessi, Hicks. Ditto: ditto (in Cambridge Museum ). 



Plate XI. 



Figs. 1,2. Bellerophon llanvirnensis, sp. nov. From Llanvirn Quarry : Upper 

 Arenig. 



3. Ophileta, sp. Ditto : ditto. 



4. Pleurotomaria llanvirnensis, sp. nov. Ditto : ditto. 



5. 6. Conularia llanvirnensis, sp. nov. Ditto : ditto. 

 7. Theca caereesiensis, sp. nov. Ditto : ditto. 

 8-10. Orthoceras caereesiense, sp. nov. Ditto : ditto. 



Discussion. 



Prof. Ramsay complimented the author on having brought forward 

 a paper so well worked out. He gave an account of his own early 

 geological work in Wales, and stated that he had mapped the rocks 

 referred to by Mr. Hicks in 1841. He differed from the author in 

 believing his supposed Laurentian rocks to be igneous. They were 

 metamorphosed Cambrian deposits which had lost all traces of their 

 aqueous origin. In 1841 no fossils had been found below the Llan- 

 deilo Flags in any part of the series described by Mr. Hicks ; and 

 then there was no ground for establishing those palseontological 



