VOL. XVII. (i) SOME GLACIAL FEATURES IN WALES 39 



masses. A moel not so glaciated is Moel Feudwy (1940 feet), 

 close to the Carmarthen Fan. 



All these cwms, it should be noticed, face between north 

 and east. Further south, between Aberdare and the Vale of 

 Neath, are the Craig-y-Llyn and the Craig-y-Bwlch : amphi- 

 theatral hollows facing north — the former with a median spur 

 separating the glacial lakelet of Llyn Fach from that of Llyn 

 Fawr (see Ordnance Survey Map : scale 2 inches to i mile : 

 sheet 26). 



Standing on the wind and grit-swept summit of the 

 Brecons, Pen-y-Fan (2905 feet), and looking northwards over 

 Brecon town, the view embraces the greater portion of the 

 heart of Wales. In the immediate foreground long finger-like 

 spurs, at first often sharpened to true aretes, but later cefn-like, 

 and the principal one eventually spreading and bifurcate, point 

 north-north-eastwards. They are very noticeable, and have 

 between them deep nants or valleys, some of U-shaped trans- 

 verse-section, leading headwards into deeply-excavated cwms, 

 whose head-walls rise sheer up in precipitous cliffs that 

 vertically cleave the summits. In pre-Glacial times it is 

 hkely that this partially river-dissected escarpment of the 

 Upper Old Red beds had a more subdued northern front. It 

 was probably characterized by the features usually attributed 

 to normal erosion, and not undercut by the agents of marine 

 planation. 



The Brecon-Beacon group was then most likely a matured 

 residual hill-mass, with rounded summits and smooth-backed 

 spurs drained by a system of rivulets, such as one would ex- 

 pect in a coarse-textured mountain district. But in Glacial 

 times the region was effectively glaciated, and moving snow 

 and ice spread outwards in all directions from the Brecon 

 Beacons as the centre. In closing glacial times, however, the 

 snow and ice lingered longest on the chilly north-north-east- 

 ward-facing slopes, and neve-reservoirs filled the valley-heads 

 of river-genesis. The debris from the Beacons, which is scattered 

 far and wide over the surrounding district, is sufficient evidence 

 of the erosive and transportive power of moving ice, and 

 the steep-cut head-walls of the cwms, the occasional moraine- 

 contained lakelets, the valley-waterfalls that cascade over the 



