W. A. Bvend — Lakes of Caernarvonshire. 405 



he also adds : " the water is, I incline to think, partly retained 

 because it lies in a rock-basin ground out by the old glacier." 

 He admits, however, that he is ignorant of the depths of the 

 tarn. Soundings of Llyn Ldwal do not support this view ; the 

 greatest depth obtained was 30 feet, but as the mass of drift at 

 the exit extends down the valley for a considerably greater 

 vertical distance than this, before rock can be traced across, it 

 seems probable that drift damming alone has operated in the 

 formation of the lake. 



Llyn Bochlwyd lies to the east of Llyn Ldwal, at a height of 

 1,800 feet above sea-level. Eamsay considers it to be "slightly 

 dammed up by moraine material." There is no opportunity of 

 sounding this tarn, but if it is a true rock-basin it must be of 

 considerable depth, as the drift at the exit is very thick. Moreover, 

 it is difficult to account for the irregular outline of the tarn on the 

 theory of glacial erosion. 



Two other small tarns in the neighbourhood were examined — 

 Llyn-y-Crom, lying above the gorge of Twll-Du, and Llyn Clyd to 

 the west of Ldwal. Kound neither of these could rock in situ 

 be continuously traced. Ffynnon-y-Lloer, beneath the summit of 

 Carnedd Dafydd, is not described by Ramsay, but drift material is 

 marked round the exit on his map. Rock in situ can, however, 

 be traced within this, but at a point about 40 yards to the north 

 of the end of the lake there is a thick mass of moraine matter, 

 and it is here probably that a dam exists, as the lake is apparently 

 shallow. 



To the south and east of the ridge terminating in Moel Siabod lie 

 two tarns — Llyniau-duwaunedd and Llyn-y-foed. The first of these 

 lies in a deep valley, across the end of which runs a ridge of rock, 

 broken, however, in two or three places by marshy and peat-covered 

 intervals, beneath which drift material might lie. Llyn-y-foed 

 at first sight looks very much like a rock-basin, rock in situ being 

 exposed nearly the whole way round ; at the south-west angle 

 of the lake, however, a deep depression, about 30 yards wide, 

 appears to be filled with drift material. 



Several features of interest are presented by the group of long, 

 narrow, and roughly parallel lakes, which lie to the north of the 

 Capel Curig and Bettws-y-Coed road, and drain into the valley 

 of the Conway. Llyn Geirionydd, the most easterly, is situated at 

 a height of 616 feet above sea-level. The western side of the lake 

 is formed by the rugged mass of Mynydd Deulyn rising abruptly 

 from the margin to over 1,300 feet. Rock in situ can be traced 

 continuously from the left bank of the outflowing stream to 

 just behind the cottage Tal-y-llyn at the head of the lake. Here 

 there is an alluvial flat about 200 yards wide, and then rock 

 is again exposed in the stream flowing from the reservoir. By 

 going a considerable distance in a south-westerly direction solid rock 

 can be traced round the tract of alluvium. The eastern shore 

 of the lake is formed by the steep grass-covered slopes of Pen-y- 

 Drum, varying from 900 to 1,000 feet in height. To the east 



