THE LAKES OF SNOWDONIA AND EASTERN CARNARVONSHIRE. 465 



Just south of Dulyn is situated another small tarn, named Melynllyn, the surface 

 of which reaches an elevation of over 2000 feet. No soundings were taken in this 

 lake ; but it appears to be very deep, and is interesting in that an unmistakable 

 morainic mound can be traced running along its eastern border. It is probably partly 

 a rock-basin and partly a barrier-basin. 



Llyniau Mymbyr. — These lakes lie at the distal end of Nant-y-Gwrhyd, and may be 

 considered as one sheet of water. The valley narrows towards the outlet, and hence the 

 flow of the ice would be here retarded. The greatest depth obtained was only 29 feet 

 — this was found in both the higher and lower portions. Though the possibility of a 

 drift-dam cannot be excluded, it is more probable that the shallow depression has been 

 formed by the erosive action of the glacier moving down the valley. 



Llyn Ogiven. — This lake lies at the head of a valley at an elevation of 984 feet. 

 Though nearly a mile long, it has nowhere a depth of over 10 feet, At one time it may 

 have been much deeper, but it is now shallowed, owing to the great amount of sediment 

 which has been carried into it. Rock can be traced right across the valley at the exit, 

 and the stream from the lake runs over this in a waterfall. Rocky cliffs border the 

 lake on either side, but at the head an alluvial flat extends upwards towards the 

 watershed. Before reaching the watershed, which consists of drift, live rock can be 

 followed across the valley, except for an interval of about 40 yards wide near Pont 

 Bodesi. It is possible that Ogwen once drained in the opposite direction towards Capel 

 Curig. But during the Glacial Epoch a great thickness of ice must have accumulated 

 on the site of the lake, for the glaciers of Cwm Bochlwyd and of Cwm Idwal descended 

 to swell the mass already gathered there. Consequently there would be a tendency 

 to erode a shallow basin under the ice. In Ogwen we have probably an example of a 

 basin produced at the head of a valley by glacial erosion during a late stage of the 

 Glacial Epoch, when the ice had retreated from the lower reaches of the valley. 



To the north-east of Capel Curig a number of long, narrow upland-valleys run 

 from south-west to north-east and drain into the valley of the Conway. In their 

 upper reaches these valleys are held in at the sides by high hills, and their floors 

 are occupied by lakes. Lower down, the valleys are wider, and are largely covered with 

 drift. The streams, on reaching the boundary of this upland district to the east, fall 

 with a steep descent into the broad and deep Vale of Conway. 



Of these lakes Llyn Crafnant almost certainly lies in a rock-basin. The valley in 

 which the lake lies is cirque-like at its head, the hills rising to heights of 1500 feet, 

 and their elevation is still greater along the sides of the lakes. The surface of the 

 water stands at an altitude of 602 feet. A.t the foot, the hills on either side approach 

 each other so as almost completely to shut in the lake. But a narrow gorge is left by 

 which the stream escapes from the lake. Rock can be seen along the margins of the 

 stream, but its bed is filled with large boulders. The water has a rapid fall through 

 the gorge, and so would probably have carried away any drift which lay in its path. 



The lake has a greatest depth of 70 feet, and the deeper contour-lines are of very 



