Vol. 6g.~] GEOLOGY OF BAEDSEY ISLAND. 527 



five localities, 1 and they all indicated movement of the ice to the 

 east of south, not to the south-west as previously supposed. The 

 suggestion quoted above that Mynydd Enlli affords an example of 

 1 crag-and-tail' structure falls, therefore, to the ground; in fact, the 

 roches moutonnees on its eastern slopes are worn parallel to 

 the trend of the ridge and not across it. 



As Dr. Jehu had already investigated the sources of the Bardsey 

 boulders, I contented myself with collecting a few specimens from 

 the boulder-clay of Porth Solfach and neighbourhood, and .sent 

 them to my friend Mr. E. Greenly for comparison with Anglesey 

 rocks and boulders, as it seemed highly probable that the ice-sheet 

 that invaded Bardsey had previously passed over Anglesey. His 

 determinations are interesting, as they enable the movement of the 

 ice-sheet to be defined very closely. Two of the pebbles are red 

 granites of typical ' Mona ' type, while a third of fine-grained 

 granite is also a Mona granite. An augen-gneiss pebble inay have 

 been derived from the Anglesey gneisses, but Mr. Greenly is more 

 inclined to regard it as derived from the Scottish Highlands. 

 Other Anglesey rocks identified are Ordovician grit and slate, and 

 white cherty shale from the top of the Carboniferous Limestone. 

 Other specimens, including Chalk-flints, occur as boulders in Anglesey, 

 and only two specimens (a purple rhyolitic felsite and a yellowish 

 grit) are unknown to him. Now, the Mona granite is practically 

 confined to a belt in Central Anglesey which has a south-westerly 

 trend corresponding with the general trend of the ice-sheet in that 

 region, and Ordovician grits and slates lie on the flank of the granite, 

 while Carboniferous Limestone lies on the north-west. The portion 

 of the Irish-Sea glacier that invaded Bardsey must, therefore, have 

 passed over Anglesey to the west of Red Wharf Bay. The course 

 of the ice-sheet across Anglesey was in a south-westerly direction % 

 and this course is now shown to have been deflected in Carnarvon 

 Bay to a direction east of south, a deflection which seems to have 

 been caused by pressure from the ice that radiated from the east of 

 Ireland. It was previously know r n that Irish ice had forced the 

 Irish-Sea ice into South Wales, across Cardigan Bay into North 

 Pembrokeshire ; 2 and it is of interest now to find that the pressure 

 has also left its traces in this little westerly outpost of North 

 Wales. 



1 The localities are : — The coast north of Mynydd Enlli ; Hen-dy ; Porth 

 Solfach, near the granite ; near Trwyn Dihirid ; and the coast east of the 

 lighthouse. 



2 See T. J. Jehu, ' The Glacial Deposits of Northern Pembrokeshire ' Trans. 

 Roy. Soc. Edin. vol. xli, pt. 1 (1904) p. 53, and previous literature quoted 

 therein. As a contribution of my own (' On the Geology of Part of North- 

 East Pembrokeshire' Proc. Birm. Nat. Hist. & Phil. Soc. vol. x, pt. 2, 1897, 

 pp. 92-101) was inadvertently overlooked in that paper, I hope that I may be 

 excused for mentioning that I had previously proved the former presence of 

 Irish-Sea ice in the north-east of that county. [Attention is also invited to the 

 Discussion, pp. 532-33, both as regards the former presence of Irish-Sea ice in 

 Merionethshire, and as to the cause of the deflection of that ice into Cardigan 

 Bay.] 



