48 DR T. J. JEHU ON 



last seen at Llanbedrog, where it forms the lower part of the cliff and the foreshore at 

 the west end of the bay. A boring indicates its presence below the modern alluvium 

 in the harbour at Pwllheli, but east of this it does not appear — the cliffs from Afon- 

 wen to Criccieth being formed entirely of the Sands and Gravels and the Upper 

 Boulder Clay. But though not exposed anywhere along this part of the coast, it 

 probably underlies these Upper Drift deposits. 



Inland the Lower Boulder Clay is rarely exposed at the surface, but it may occa- 

 sionally be seen underlying the marshy low grounds and moors or along the banks 

 and beds of streams which have cut through the Upper Drift deposits, as, for instance, 

 along the Afon Horon, below Nanhoron. Even where there are no exposures at the 

 surface, borings and artificial cuttings prove it to be present under the other deposits. 

 At Ty-Cam, Four Crosses, north of Pwllheli, it was found resting on a shattered surface 

 of rock. Above the rocky cliffs at Porth Pistyll, south-west of Aberdaron, it is seen 

 resting on the bed-rock at a height of over 100 feet above the sea-level. In other 

 borings inland the bottom of this clay is not reached, but at Tydweiliog some sand was 

 reached lying in or below the Boulder Clay. Shell-remains were not observed in the 

 Boulder Clay away from the coast, except doubtfully in the brickfield at Llanor, north 

 of Pwllheli. But the inland sections and exposures of this clay were too poor to render 

 any adequate search for shell-remains or erratics possible. All that can be stated with 

 certainty is that Boulder Clay underlies the sands and gravels in the interior as well as 

 on the coast, and that this clay is of a dark bluish-grey colour and is very tenacious and 

 compact ; that in some places it is full of boulders, many of which are well glaciated, 

 and at others fairly free of boulders. The included boulders are most numerous in the 

 eastern part of the district which approaches the mountains of Snowdonia, and these are 

 mostly of Welsh origin. The Lower Boulder Clay has all the characteristics of a true 

 bottom-moraine, and is undoubtedly the product of an ice-sheet which came from the 

 north and invaded Western Carnarvonshire after having made its way over the bed of the 

 Irish Sea and passed over Anglesey. The direction of transport of the included erratics, 

 the configuration of the glaciated hills and the roches moutonnees, and the course of the 

 rock-strise all indicate that the movement of the ice was roughly from north-east to 

 south-west. Professor James Geikie, in his classic book — The Great Ice Age — gives a 

 map of the British Isles during the Epoch of Maximum Glaciation in which he depicts 

 this mer de glace as overwhelming Anglesea, skirting the north-west coast of Carnarvon- 

 shire, and passing south-westwards over the tip of the Lleyn peninsula. The late Mr 

 Carvill Lewis, on the other hand, in a sketch-map which is reproduced in Professor 

 Bonney's Ice Work (1896), p. 18G, makes what he terms the Irish Sea Glacier terminate 

 in an edge parsing along and just within the north-west boundary of Lleyn westwards 

 towards Ireland, leaving the south of the Lleyn peninsula and Cardigan Bay outside its 

 boundary. The facts recorded in this paper prove that this great ice-sheet covered the 

 greater part of Western Carnarvonshire, passing over Lleyn into Cardigan Bay. 



In a previous paper communicated to this Society, the writer proved that this 



