THE GLACIAL DEPOSITS OE WESTERN CARNARVONSHIRE. 19 



rearranged material derived from the bottom moraine of an ice-sheet which reached 

 this elevation. 



Mr T. Mellard Reade, in a paper on " The Drift Beds of the Moel Try fan Area of 

 the North Wales Coast," * describes the coast sections from Dinas Dinlle to Nevin and 

 also some sections inland. He favours the view that the sands and gravels are marine, 

 and that they indicate a submergence of this area in Glacial times to at least 1400 feet. 



The base of the Lleyn promontory lies just outside the mountains of Snowdonia, and 

 has a breadth of about 5 miles. South-westwards the breadth varies from 3 to 5 miles, 

 becoming reduced to about a mile at the extreme end. None of the great valleys of 

 Snowdonia trend towards Lleyn. The stratified rocks of this district are chiefly of 

 Lower Silurian (Ordovician) age, and through these protrude a number of igneous masses 

 which form an interrupted chain of hills along the whole extent of the promontory. 

 Hard grits and shales of Cambrian age constitute the high ground between Porth 

 Nigel and St Tudwal's Eoad, and metamorphosed rocks which are now regarded as pre- 

 Cambrian extend from Porth-dinlleyn to the end of the promontory and form the Isle 

 of Bardsey. These metamorphic rocks rise to heights of 500 feet at the extreme end of 

 Lleyn. The lower parts of the district are covered by a mantle of Drift, and if this were 

 entirely removed considerable parts of Lleyn would probably be submerged. 



II. The Coast Sections. 



The following account of the superficial deposits begins with the sections at Dinas 

 Dinlle and the coast is followed south-westward to the end of Lleyn and thence 

 eastwards on the south side of the promontory to Criccieth. 



From Dinas Dinlle south-westwards as far as Gwydir Bay the coast-line is for the 

 greater part bounded by cliffs of varying heights which are described on the Geological 

 Survey Map (1 inch to the mile) as consisting of stratified clay, sand, and gravel. The 

 bed-rock is not seen anywhere along this stretch of coast. 



To the north of Dinas the coast is flat, consisting of alluvial land which extends 

 towards the entrance of the Menai Straits. The character of this flat area is shown by 

 a boring recently made for water a few yards behind the hotel at Dinas. Eighteen feet of 

 grey sand were passed through, in which the shells of Cardium edule were abundant, 

 as well as the shells of Scrobicularia piperata, with the two valves often still in apposi- 

 tion. This sand is evidently a recent marine deposit. Below the sand a very tough 

 bluish-grey boulder clay was reached, and this extends to an unknown depth. 



Dinas Dinlle. — This is a dome-shaped mound surmounted by an ancient encamp- 

 ment. One side of the mound is being cut away by the sea, so that good sections, 

 which have been described by Mr T. Mellard Reader are exposed. The cliff varies 

 in height up to a maximum of about 100 feet. 



* Proc. Liverpool Geol. Soc, vol. vii. (1893), p. 36. 

 t Ibid., p. 42. 



