THE GLACIAL DEPOSITS OF WESTERN CARNARVONSHIRE. 35 



Hazel-nuts were found in the peat, and the bark of birch trees. A little rubble rests 

 on the rocky slope at the end of the bay, but its relation to the Lower Boulder Clay is 

 obscured by slipping. 



Amongst the shells and fragments of shells gathered from the Lower Boulder Clay 

 at Porth Nigel the following have been identified : — 



Gasteropoda. 



Ttcrritella communis, Lam. 



Buccinum undatum, L. 



Tritonofusus gracilis, Da Costa. 



Murex (Ocinebra) erinaceus, L. 



Purpura lapillus, L. 



Trophon {Boreotrophon) dathratus, L. 



Trophon [Boreotrophon) scalar iformis, Gould. 



Lamellibranchia. 



Pectunculus glycimeris, L. 

 Mytilus edulis, L. 

 Astarte sidcata, Da Costa. 

 Astarte (Nicania) compressa, Mont. 

 Astarte (I'ridonta) arctica, Gray. 

 Cyprina islandica, L. 

 Tellina (Macoma) balthica, L. 

 Mactra (Spisula) solida, L. 

 Venus (Venfricola) casina, L. 

 Gard.ium edule, L. 

 Mya truncata, L. 

 Corbula gibba 1 Olivi. 

 Nucidana, sp. 



A cirriped was also found in the ciay. # Complete specimens of Murex erinaceus and 

 Tumtella communis were obtained, and complete single values of Astarte sulcata and 

 A. compressa. 



Porth Ceiriad is situated at the end of the promontory which separates Porth Nigel 

 from St Tudwal's Road. This bay opens to the south, and is carved out of the hard 

 gritty sandstones and shales of Cambrian age between Penrhyn-du and Mynydd Cilan. 

 It is nearly a mile broad. The Lower Boulder Clay is not exposed in this bay. The 

 cliff attains heights of 50 to 60 feet, and slopes away inland at the top. It consists of 

 yellowish weathered Drift with boulders which are subangular in shape, and many of these 

 show ice-scratches. Beds of pebbly material and sand are seen lying in or below the above, 

 and even in places extending to near the top of the cliff. Toward the top, however, 

 the Drift is usually rubbly in character. At the two sides where the rocky cliffs come 

 in ; the Drift is separated from the bed-rock by a mass of rubble or " Head." Large 

 boulders derived from the cliff lie on the beach, and these are chiefly of local Welsh 

 rocks, but specimens of the reddish-streaked rhyolite are fairly common. 



St Tudwal's Road. — The only place where the Drift is exposed is at the south- 

 western end, where it consists of a rubbly clay, yellowish and weathered. This probably 

 belongs to the Upper Boulder Clay horizon. The whole of this bay, with the exception 

 of the rocky promontory and the estuary at Abersoch, is bordered by sand dunes. At 

 the back of the sand dunes marshy land occurs at some places, as at Cors Llyferin, and 

 this is probably underlain by Boulder Clay. The promontory on which a part of 



* For the determination of these and other shells mentioned in this paper the writer is indebted to Mr Henry 

 Woods, M.A., Lecturer in Palaeontology at the University of Cambridge. 



