Vol. 69.] GEOLOGY Of'bARDSEY ISLAND. 515- 



II. History of Previous Researches. 



Oar present knowledge of the geology of this island is derived 

 from the Geological Survey 1-inch map (quarter-sheet 76, 8.) and 

 from short descriptions to be found iu the following works : — 



1843. Sedgwick, A. — 'Outline of [the] Geological Structure of North Wales' 



Proc. Geol. Soc. vol. iv, p. 213. 

 1866. Ramsay, A. C— ' Geology of North Wales ' Mem. Geol. Suit. vol. iii, 



pp. 169-70 ; also 2nd ed. (1881) p. 212. 

 1888. Blake, J. F.— ' On the Monian System of Rocks' Q. J. G. S. vol. xliv. 



p. 531. 

 1893. Raisin, Miss C. A. — 'Variolite of the Lleyn & Associated Volcanic 



Rocks' Q.J. G. S. vol. xlix, p. 160. 

 1909. Jeihj, T. J. — 'The Glacial Deposits of Western Carnarvonshire ' 



Trans. Roy. Soc. Edin. vol. xlvii, pt. 1, pp. 28-29. 



Sedgwick grouped the rocks of Bardsey with those of the coastal 

 strip of the neighbouring mainland as ' chlorite and mica-slate,' 

 and correlated them with ' a formation which is widely expanded 

 in the Isle of Anglesea' (op. supra cit. p. 213). As regards their 

 position, he considered that they were ' inferior to the other slato 

 rocks in the southern promontory of Carnarvonshire' (ibid. p. 219). 

 The island was mapped (about 1850) by Mr. A. II. Selwyn, whose 

 MS. notes supplied the information for the following short account 

 given in Eamsay's Survey Memoir of 1866, in which the beds are 

 classified as ' metamorphosed Cambrian ' : — 



'Bardsey. — The east coast of Bardsey Island consists of "green, grey, and 

 purple siliceous schists and slaty rocks, patches of quartz rock, and a few thin 

 grey calcareous bands, all much contorted on a small scale, without affecting 

 the general north-westerly dip." A lenticular piece of marble occurs on the 

 coast about half way between Ogof-Morlas and Pen Oristih. At Bay-y-Nant 

 tbe dip is easterly. On the west the rocks are of the same description. The 

 whole undulates in various contortions ' (pp. 169-70). 



In the 2nd edition Sir Andrew Banisay added that the rocks 

 ' chiefly consist of highly metamorphic strata of a rudely gneissic 

 character.' He also gave a short account of the glaciology of the 

 island. 



Blake placed the Bardsey rocks in the ' Volcanic Facies ' of his 

 Monian System. He records ' large agglomerates with calcareous 

 and quartzose patches ' on the eastern side of the island ; and ' on 

 the slope of the hill and by the lighthouse, low quartz-knobs of the 

 usual isolated form and characteristic structure.' 



Miss Baisin's description, given after a ' somewhat hurried ' 

 examination, refers to the agglomerate, tuff, and green diabase at 

 the extreme southern point and to ' well-banded ashy rocks ' in 

 the same neighbourhood ; draws attention to the ' coarser ag- 

 glomerates (including large compact blocks and streaky laterite) 

 which ' can be seen from a boat to ' form the eastern cliffs north 

 of Yr-Henllwyn ' ; and mentions the discovery of a granitic or 

 granitoid rock at three localities. She regards the rocks in the 

 main as part of a volcanic series, those in the south being. 



