•528 DR. J. S. FLETT ON THE [Oct. I913, 



VII. The Post-Glacial Eaised Beach ('?). 



The isthmus between Porth Solfach and Henllwyn forms the 

 lowest part of the island, with a level about 18 to 20 feet above 

 Ordnance datum. The low cliffs on each side are excavated iu 

 boulder-clay, on which lies at several places a shingle resembling a 

 thin beach-deposit. I also found sand containing marine shells in 

 •one of the fields about here. It seems not unlikely, therefore, that 

 we have at this spot a relic of the post-Glacial 25-foot beach so 

 well-known on the east coast of Ireland ; but the evidence is, to my 

 mind, not strong, and I should like to have confirmatory evidence 

 •of a similar beach on the neighbouring mainland of North Wales 

 before definitely adopting this explanation. Oue would expect, for 

 instance, that when the sea was at raised-beach level the scour of 

 ■the tides between the two islands into which Pardsey would have 

 been divided would have swept out the boulder-clay. One has also 

 to consider the possibility that the shingle and sand may in recent 

 times have been cast over the isthmus during storms, or even that 

 the shingle may have been spread artificially along shore cart-tracks 

 now cut into by coast-erosion. 



Mr. Pearnsides has recently recognized some features on the 

 coast east of Criccieth. which suggest to him a post-Glacial rock- 

 platform about 10 feet above tide-level. 1 This level corresponds 

 fairly well with that of the Pardsey platform, so that further work 

 in the Lleyn may establish a post-Glacial raised beach in Pardsey 

 beyond reasonable doubt. 



In conclusion, I wish to express my warmest thanks to Dr. J. S. 

 Plett for undertaking the examination of the rocks and for con- 

 tributing an Appendix on the Petrography, and to Mr. Greenly for 

 his comparison of the Pardsey drift-pebbles with Anglesey rocks 

 •and boulders. My best thanks are also due to Mr. Herbert H. 

 Thomas, Sec.G.S., for supervising the preparation of the colour- 

 printed map, and to the Assistant Secretary for his care in seeing 

 the paper through the press during my absence in India. 



VIII. Appendix on the Petrography. [J. S. P.] 



(1) The Granites. 



The granite that forms the sills or veins on Pardsey Island is 

 pale, usually greyish green from the abundance of chlorite. It is 

 neither coarsely crystalline nor porphyritic, and all the specimens 

 examined have a crushed or broken appearance, although there is 

 nothing like a well-developed or regular foliation. Occasionally, 

 the granite is so much shattered, with broken felspar-crystals lying 

 in a dark-green chloritic matrix, that it becomes very similar in 

 appearance to a crushed felspathic grit [9090, Porth Solfach]. 



1 'The Treinadoc Slates & Associated Eocks of South-East Carnarvonshire' 

 Q. J. Gr. S. vol. lxvi (1910) p. 184. 



