154 Henry Dewey — Land-forms in Caernarvonshire. 



infilled with glacial deposits, and the plain and even the tops of hills 

 carry boulder beds. This evidence clearly indicates that the vpide 

 general topography as it at present exists was for the most part 

 produced in pre-GIacial times, or at least when the spreads of glacial 

 detritus were laid down. 



The 430 foot Plain. 



By keeping to the Ogwen Valley, however, a wrong impression of 

 the topography of Caernarvonshire is gained, and it comes as 

 a surprise to find, after climbing the hills, not a mountain region, 

 but a widespread area of gently undulating ground, p. 150 (Fig. lb), 

 where the hills are truncated into flat-topped ridges. On turning 

 towards the mountains it is further seen that this plain abuts against 

 their masses at an even level for many miles, while they rise from it 

 like islands from the sea. 



-'^^f^: 



V> 







Fig. 2. — The " Pliocene " plateau near Bangor. The plain terminates at 

 a height of 430 feet above sea-level, the mountains near Snowdon rising 

 abruptly from it. Its wide expanse is clearly seen in this sketch. 



The above picture (Fig. 2} shows a view of these features taken 

 from the Bangor Golf Links and looking towards Nant Ffrancon. 

 where the wall-like mass of Glyder Fawr is seen bounding the valley 

 at right angles to it. 



Another sketch (PI. VII, Fig. 3). made near the Anglesey 

 Monument, shows similar features of a country diversified into 

 a series of parallel ridges with flat tops, terminating against the 

 mountain mass. In the area bpunded by the Ogwen Valley, the 

 Padarn Valley, and the mountains there is scarcely a hill that rises 

 above this plain, although much of the ground is lower and there are 

 several deep river-valleys. The amount of erosion that has taken 

 place since the uplift of the plateau is marked by the Menai Straits, 

 which attain a depth of 70 feet below sea-level, while the Afon 



