THE GLACIAL DEPOSITS OF WESTERN CARNARVONSHIRE. 25 



In the stoneless sands pockets of gravel occur. The sands and the finer gravels show 

 beautiful examples of oblique bedding. These false-bedded sands and gravels can be 

 traced for some distance in the lower part of the cliff. The sands are very fine and marine- 

 like, and apparently form the greater part of the cliff. Just before reaching the road that 

 comes down to the beach the Lower Boulder Clay is again seen at the base. West of 

 the road the cliff is still obscured by vegetation, but appears to be made up mostly of 

 sand. At this part of the bay there has been much sliding over the unctuous Lower 

 Boulder Clay, giving rise to an under-cliff. The under-cliff is made up of the lower stiff 

 clay, and above it the cliff slopes away and is grassed over. The upper part consists of 

 yellowish sandy clay full of small boulders. The Lower Boulder Clay is here very dark 

 in colour, and presents a striking contrast to ail the deposits above. 



Promontory of Porth-dinlleyn. — A rocky shelf can be seen on the eastern side 

 appearing from under the Drift. It has a glaciated aspect where the deposits have 

 been recently cleared away. The shelf or platform is well seen just before reaching 

 the lifeboat house. At its inner (landward) end it is 15 feet above the modern beach 

 and slopes gently seawards. The sea is gradually eating into and destroying it. Just 

 beyond the lifeboat house the serpentinous rock shows distinct marks of glaciation — 

 the grooves and scratches running approximately N.E. and S.W. Near the extremity 

 of the promontory, north-east of the flag-staff, at a height of 25 feet above Ordnance 

 datum, the rock is beautifully glaciated, showing deep and broad furrows and ice- 

 scratchings running about N.E. and S.W. These are the finest glacial markings noted 

 by the writer in Lleyn. 



The following far-travelled boulders were found in the Gravel and Sand series at 

 Porth Nevin and Porth-dinlleyn : — 



Several granites from the Dalbeattie area ; a granite with reddish idiomorphic 

 felspars much resembling the Shap granite ; the Ailsa Craig micro-granite. The shell- 

 fragments in the sands were, as a rule, too broken and minute to be identified, but the 

 following forms were obtained : — Turritella communis (Lam.), Nucula nucleus (L.), 

 Pecten (Chlamys) islandicus ? (Mull), Astarte sulcata (Da Costa), Cyprina islandica 

 (L.), Cardium edule (L.). 



On the west side of the promontory lies the little bay which bears the name of 

 Porth Wen. Here the Drift is again exposed in sections which are 40 to 50 feet high. 

 The stiff bluish-grey Lower Boulder Clay forms the base of the cliff, and is succeeded 

 above by fine yellow marine-like sands and some gravel. 



From this bay to Porth-ysgadan the coast is rock-bound. Some Drift caps the rocky 

 cliffs and is usually overgrown with grass. 



Porth-ysgadan. — Fairly good sections of the Drift deposits are seen at this place. 

 Opposite the middle of the bay the typical Lower Boulder Clay with included shell - 

 fragments forms the lower part of the cliff, and the bottom of this deposit is not 

 reached in the section. Above, the face of the cliff slopes away and is grassed over, 

 but there are indications that sand overlies the Boulder Clay. The upper part consists of 



TRANS. ROY. SOC. EDIN., VOL. XLVII. PART I. (NO. 2). 4 



