THE ANCIENT EOCKS OF ST. DAVID'S. 179 



sion, the beds are repeated, and afterwards lost on the north coast. 

 Lithologically this subgroup differs considerably from that immedi- 

 ately underlying it, and also palaeontologically sufficiently to warrant 

 its being considered a distinct series. In 1841 the species Lingula 

 Bamsayi, Bellerophon perturbatus, and Calymene duplicata were 

 found in these slate- quarries by Prof. Ramsay and Mr. M'Lauchlan ; 

 but many additional species have since been discovered in the series. 

 The fossils are very much distorted by cleavage ; and it is difficult in 

 consequence to obtain good specimens; the most characteristic 

 species in this subgroup are Ogygia Buchii, Calymene duplicata, 

 Cheirurus Sedgwickii, Trinucleus fimbriatus, Ampyoc nudus, Bar- 

 randea Cordai, &c. 



The Llandeilo group, wherever exposed in South Wales, shows 

 almost exactly the same order of the strata as in this section at 

 Aber-eiddy. In the so-called typical districts of Llandeilo and 

 Builth there are no rocks of older date than the tuff beds of the Lower 

 Llandeilo ; nor have the characteristic fossils even of this series been 

 found there ; but the lithological evidence indicates the presence of 

 the series in each place, and the fossils may doubtless be found 

 there if carefully searched for. The calcareous or Middle Llandeilo 

 beds are well seen in many parts of Carmarthenshire and Breconshire ; 

 and it was to this series that the name Llandeilo was first applied. 

 The Upper Llandeilo occurs also in Carmarthenshire and near Builth, 

 in Breconshire ; and most of the fossils characteristic of the beds 

 in Pembrokeshire have been found there. In Shropshire the whole 

 Llandeilo group occurs in succession to the Upper Arenig, and the 

 usual fossils are found in each of the series. In North Wales the 

 Lower Llandeilo is found in the Arenig Mountains, in the Pfestiniog 

 Mountains, and in the Arans, resting conformably on the Arenig 

 group; but the evidence of the occurrence of the Middle and 

 Upper Llandeilo series in these districts is still incomplete. The 

 fossils, however, which have been found in beds on the east side of 

 the Arenigs, and on the east of the Berwyn Hills, show that they 

 are not entirely absent ; and further examination will most likely 

 prove the presence of a succession there very like that which has 

 now been made out in South Wales. 



List of Fossils from the Llandeilo Group, Pembrokeshire. 



Lower Llandeilo. 



Name. Localities. 



Trinucleus Earnsayi, Hicks Cliffs south side of Aber-eiddy Bay. 



Calymene Murchisoni ?, Salt Ditto. 



Ogygia, sp Ditto. 



iEglina, sp. Ditto. 



Lingula attenuata, Sow t Ditto. 



Siphonotreta, sp Ditto. 



Bellerophon perturbatus, Sow Ditto. 



Theca caereesiensis, Hicks Ditto. 



Didymograptus Murcbisoni, Leek Ditto. 



, var. geminus Ditto. 



■ , var. furcillatus Ditto. 



Q. J. G. S. No. 122. . q 



