83 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



These are the chief localities whence the history of the Tre- 

 madoc rocks of North Wales has been drawn and deduced, from 

 which also their remarkable fauna has been disentombed, and that 

 mainly through the instrumentality of Mr. David Homfray and Mr. 

 Ash of Portmadoc, the late Mr. Salter, and the old collector for the 

 Survey, Mr. Gibbs. 



The careful and thorough examination of North and South Wales 

 that has of late been made by so many able observers, has clearly 

 shown the perfect sequence and agreement in stratigraphical suc- 

 cession between the whole of the groups ranging from the Har- 

 lech and Longmynd strata to the Llandeilo ; this is complete for 

 South Wales in the St.-David's promontory as one continuous and 

 ascending section, with no break in continuity. It is not so clear 

 or complete a sequence in North Wales, where the chief localities 

 for the Tremadoc and Arenig groups are more widely separated, 

 both formations being only developed in two counties in North 

 Wales, viz. Merionethshire and Caernarvonshire — the Lower Tre- 

 madoc series chiefly at Penmorfa, Borthwood, and Llanerch in 

 Caernarvonshire, and in Merionethshire at Cae Iago near Maentw- 

 rog and at Tyn-y-llan. The Upper Tremadoc rocks, on the contrary, 

 are best developed in Merionethshire at Tuhunt-y-bwlch, Penclo- 

 gwyn, and Garth, whilst Moel-y-gest is the only locality in Caernar- 

 vonshire where they occur. The Arenigs, which also occur only in 

 the same counties, I shall have occasion to refer to at considerable 

 length when speaking of the distribution of the species. 



The discovery near St. David's, by Hicks and Salter, of Tremadoc 

 slates equivalent to those of North Wales threw new light upon the 

 history of that remarkable promontory. Not only are these slates 

 the same as those of Merioneth and Caernarvonshire, but a large 

 number of additional species of much interest have been added to the 

 whole fauna. In 1866* Messrs. Hicks and Salter published the results 

 of their researches at St. David's, giving a list of the species dis- 

 covered by them. Since then Dr. Hicks has reaped a large harvest 

 of new forms from these rocks, thus adding to the history and 

 palaeontology of that area — no less than thirty species having 

 occurred to him. These were obtained from three distinct loca- 

 lities — the first on the north-eastern coast of Eamsey Island ; 

 the second at the northern extremity of Whitesand Bay, and ex- 

 tending 4 miles in a north-easterly direction beneath the Arenig 

 rocks ; the third at Tremanhire, an extensive area or tract 5 miles 

 east of St. David's, thus showing extensive geographical distri- 

 bution. The Ramsey-Island section is stratigraphically complete, 

 having for its conformable base the Lingula-flags full of Linguiella 

 Davisii ; and upon the intervening Tremadoc rocks, here 1000 feet 

 thick, succeed the Arenigs, thus here, as at Whitesand Bay, affording 

 clear proof of the intercalated position of the Tremadoc group. In 

 North Wales no Arenig rocks are known to rest directly upon the 

 Tremadoc anywhere. Dr. Hicks obtained in all 29 species from 

 the Pamsey-Island section, 24 of which were new; and 15 occurred 

 at Tremanhire, inland, east of St. David's. 



* Brit. Assoc. Eeport, 1866, p. 182. 



