Henry Deivey — Land-forms in Caernarvonshire. 147 



North Wales was perliaps the first district where the former 

 presence of glaciers was inferred from the characters of its land- 

 forms. Darwin and Ilamsay both described examples of such forms 

 near Nant Ffrancon as were then acknowledged to be due to glacial 

 action, namely the moraines, perched blocks, rochesmoutonnees, lakes, 

 and the general U-shaped sections of the Talleys. Since then other 

 land-forms have been recognized as equally significant of glacial 

 agencies, such as aretes, cirques, gendarmes, valley steps, and 

 hanging valleys. Professor Garwood ^ has described typical instances 

 in the Ticino Valley. Now all these features are preserved in North 

 Wales, but perhaps nowhere in so characteristic a manner as in the 

 Nant Ffrancon district. Further, their relationship to earlier land- 

 forms is equally well revealed in this neighbourhood, and for these 

 reasons the district is one of particular interest to all students of 

 georaorphology. 



In the following account each feature is described as it is met with 

 in following the valley from the water-divide downwards to its 

 confluence with the sea. 



The Ogwek Yallet. 



The Afon Ogwen rises on the southern slopes of Carnedd Dafydd 

 as a turbulent mountain torrent, the Afon Dena, and dashes down- 

 hill among rocks and boulders in a series of rapids and cascades, 

 pursuing a course roughly parallel with a neighbouring stream that 

 afterwards flows in a diametrically opposite direction. Near Pont 

 Ty-c6ch the two streams reach flat land partly covered with glacial 

 drift and peat, but beneath these superficial deposits lie solid rock 

 scored deeply with strise and worn into roches moutonnees. This 

 low ground, although apparently flat, is the water-divide between the 

 Rivers Ogwen and Llugwy, and from whatever point it is viewed 

 appears to be a valley occupied by a sluggish river, which might be 

 flowing in either direction. 



The Lakes. 



The Ogwen next flows through marshy ground for a distance of 

 three-quarters of a mile, and then swells out into a lake, Llyn Ogwen 

 (PI. VII, Fig. 1). This sheet of water, nearly a mile in length, is 

 broadest at its eastern end and narrows towards the west, where its 

 waters, escape through a gorge. The total area covered by it is 

 approximately 456,400 square yards, but in spite of its size the lake 

 is remarkable for its extreme shallowness, the water nowhere, 

 attaining a greater depth than 10 feet. It is also noteworthy that 

 it is deeper at the eastern end than at the west, the gradient of the 

 lake-bottom sloping towards the east.^ It is a picturesque lake,, 

 surrounded as it is by noble mountains (PL VII, Fig. 1) that form the 

 highest group in North Wales, and is apparently landlocked. On its, 

 northern banks rise the crags of Carnedd Dafydd, with a perfect cwm 

 facing east near its summit, and in which lies the small lake. 



■" " Features of Alpine Scenery due to Glacial Protection " : Geographical 

 Journal, 1910, pp. 310-39. 

 " Jehu, op. cit., p. 440. 



