22 DR T. J. JEHU ON 



Just west of Aberafon the cliff face is again somewhat hidden by overgrowth. But 

 it can be seen to be formed of laminated stoneless sands and gravel, with some of the 

 Upper Stony Clay on top. Immediately north-east of the wooden pier the cliff attains 

 a height of about 90 feet. The upper 20 or 30 feet are made up of the Stony yellowish 

 Clay, and the rest of the cliff of very fine stoneless sands. As traced laterally the stone- 

 less sands in this upper part tend to pass into gravels and boulder gravel — the sands 

 still forming the lower part of the cliff down to its base. 



Along the whole stretch of coast from Point Maen Dulan to the wooden pier at the 

 north-east end of Gwydir Bay the stiff bluish-grey Lower Boulder Clay was not seen. 

 But in Gwydir Bay, just south-west of the pier, the Lower Boulder Clay appears again 

 at the base of the cliff. It is very tough and homogeneous, and its dark bluish-grey 

 colour is strongly contrasted in certain lights with the light-coloured yellow deposits 

 above. It is exposed all along this bay, and, on account of its unctuous nature has 

 been the cause of much land-slipping, resulting in the formation of a sort of under-cliff. 

 This under-cliff is 10 to 15 feet in height, and above it is a gentle slope much grassed 

 over. At the east end of the bay the Lower Boulder Clay is seen to be overlaid by 

 gravelly material and this again by the Upper Till. How much of the Lower Boulder 

 Clay lies under the grassed slope it is difficult to ascertain. The base of this clay is not 

 reached in the cliff sections ; indeed, the foreshore is underlaid by this tough sticky 

 clay, from which the remains of sedges or reeds are often seen protruding. Shell-frag- 

 ments occur sparingly in the Lower Boulder Clay, but they were too small for identifica- 

 tion. Boulders of Carboniferous Limestone, beautifully glaciated, occur plentifully in 

 the Lower Boulder Clay, chalk-flints are not uncommon, and porphyrites from the 

 Dalbeattie area were obtained. 



To the west of Gwydir Bay the coast is rock-bound. The cliffs of Trwyn-y-tal are 

 composed of sedimentary rocks of Lower Silurian (Ordovician) age. Considerable 

 erosion has gone on since the Glacial period. There are no traces of a raised 

 beach platform, but the almost perpendicular post-glacial cliffs are truncated above 

 by a rounded slope very similar to that described by Messrs Wright and Muff 

 on the south coast of Ireland.* Along this part of the coast, as on the south of 

 Ireland, the slope above can be seen to be continued on stacks now separated from 

 the mainland. 



To the south-west of Trwyn-y-tal there is a remarkable small dry valley which 

 opens seawards above the cliff. It evidently marks an old overflow channel. Some 

 drift is seen here in the cliffs, but the Lower Boulder Clay appears to be absent. 



Passing south, the coast is bound by the igneous mass of Yr Eifl (The Rivals), and 

 other igneous rocks of a similar nature form headlands to within a mile of Nevin. But 

 at Porth-y-nant small bays have been eroded in the softer sedimentary rocks which reach 

 the coast between the harder igneous masses. In these bays Drift deposits occur and 

 form the cliffs, but the exposures are not good. At the north-eastern end of Porth-y- 



* Scientific Froc. Royal Dublin Soc, vol. x. (N.S.), part ii., 1904, p. 296. 



