THE GLACIAL DEPOSITS OF WESTERN CARNARVONSHIRE. 39 



origin, but erratics such as far-travelled granites and chalk-flints are occasionally found. 

 In these hillocks and ridges the material is generally more or less rounded. 



The Drift of the plain rises on the flanks of the higher hills to heights of about 600 

 feet. But patches of glacial accumulations are met with at much greater heights. On 

 Y Gyrn Goch, south-west of Clynnog Fawr, Drift occurs up to a height of 1200 feet 

 above sea-level. It consists of yellowish clayey sand in which, however, no traces of 

 marine shells were found. Mr Mellard Re ade notes the occurrence of "splendidly 

 polished quartz-grains in the angular semi-decomposed gravel from near the summit of 

 the Pass between The Rivals and Mynydd Carnguwch, about 800 feet above sea-level." # 



As we pass west of a line taken as running from Clynnog Fawr to Pwllheli, the 

 moraine-like mounds and esker-like hills and ridges tend to disappear. The gravels and 

 sands continue, however, to cover much of the land and to form a mantle over the lower 

 hills. The sands tend to become fine, and are more marine-like in aspect. The fiats 

 and hollows are underlain by Boulder Clay. The hills in the neighbourhood of Nevin, 

 as, for instance, Garn Bodvean, which attains an altitude of over 900 feet above sea-level, 

 have a distinctly moutonneed aspect, and were during the Glacial period buried under 

 the ice-sheet which moved from north-east to south-west. Exposures of the Drift are 

 few in number and very poor in the western part of Lleyn, and boulders which at one 

 time dotted the surface have for most part been cleared away. Beginning at the 

 eastern end of the area investigated, the following notes were made of such exposures as 

 could be found inland. 



Poat-Cryehddivr, nearly a mile south of Llanllyfni. Mr Mellard Reade found a 

 fragment of Eskdale granite, a Brachiopod from a Carboniferous shale, and fragments of 

 schists probably from Anglesey in typical till exposed at a level of 400 feet above the 

 sea on the right-hand side of the stream Afon-ddu, just above the bridge. Sections in 

 the neighbourhood of Llanllyfni, made in driving headings in slate-quarrying operations, 

 show boulder gravel lying upon hard buff-coloured clayey till. 



Again, Mr Reade found far-travelled granites, one of which was located as from 

 Eskdale, in loamy and gravelly material seen in a section 30 to 40 feet high on the 

 right bank of the Afonddu, below Pont-Crychddwr, 350 feet above the sea. 



On the right bank of the Avon Llyfni there is a good section 35 feet in height 

 showing sandy clay full of boulders and gravel. 



Near the railway station at Penygroes Mr Reade describes t "a large mound of 

 Drift, the major axis of which is one-third of a mile long, the direction being approxi- 

 mately north and south." The width of this mound is about 200 yards. The mound 

 is composed largely of rounded stones, with sand and fine gravel, and stiff clay occurring 

 in it irregularly. This can be seen in a gravel-pit by the roadside on the way to Pont- 

 y-Cim. Between Pont-y-Cim and Y Foel there lies a circular mound of Drift known as 

 Craig -y-ddinas which has a height of about 40 feet above the road. It consists largely 

 of boulder gravel and fine gravel often with a clayey matrix. The mound is surmounted 



* Proc. Liverpool Geol. Soc, vol. vii. (1893), p. 45. t Ibid., p. 48. 



