436 MR T. J. JEHU ON 



a little more than a mile lower down in the waters of Llyn Cwellyn. Llyn Cwellyn, or 

 Cawellyn as it ought to be spelt, is a fine lake, nearly a mile and a quarter in length, 

 with Snowdon rising on one side aud Y Mynydd Mawr on the other. The main axis 

 lies in the same direction as the valley — from south-east to north-west. This lake is 

 wider than any of the other lakes of Snowdon, and a fairly uniform breadth is main- 

 tained from its head downwards to near its lower end, where it narrows a little. The 

 river Gwyrfai flows in at the upper end, a short distance from the left margin. Other 

 tiny streamlets run in further to the right, and several, coming down the slopes of 

 Snowdon on the one side and of the Mynydd Mawr on the other, also find their way 

 into the lake. The river Gwyrfai escapes again at the foot of the lake, and runs for about 

 half a mile over an alluvial fiat as far as Nant Mill, where it falls over rock. An alluvial 

 flat also extends from the head of the lake for a quarter of a mile up its valley, so 

 originally the lake must have been quite two miles long. At present the length of the 

 lake is 2120 yards, and its greatest width is 665 yards. The area covered by its waters 

 is 1,069,600 square yards, and its mean breadth is 505 yards, this being 24 per cent, of 

 the length. The hill sides rise steeply from the left shore to heights of over 1000 feet. 

 On the right the slope is a little more gentle, and the 500 feet contour-line lies farther 

 off from the shore. The lake-margin on the Mynydd Mawr side is nearly straight, but 

 on the Snowdon side the shore-line is more wavy and irregular. The valley narrows 

 towards the lower end of the lake, and at Nant Mill, where the alluvial flat ends, the hills 

 close in from both sides, a rocky barrier extending right across the valley, over which 

 the river falls in a cascade. 



Llyn Cwellyn abounds with the red char, a fish said to be peculiar to Alpine lakes. 

 This fish also thrives in the lakes of Llanberis, but does not occur in any of the other 

 lakes of this district. 



The surface of Llyn Cwellyn is, according to the Ordnance Survey Maps, 463*6 feet 

 above sea-level. The lake was sounded on 28th August 1900. The conditions for 

 carrying on the work were most favourable until towards the close of the day, when a 

 strong wind arose, blowing up the lake, in consequence of which the courses taken across 

 the lake near its upper end deviated somewhat from a straight line. 



Twelve sections were made, and these included in all 217 soundings. The greatest 

 depth observed was 122 feet, and this was found about a fourth of the way from the 

 lower end of the lake. The bulk of the water contained in the lake is estimated at 713 

 million cubic feet, and the mean depth at 74 feet, being 61 per cent, of the maximum 

 depth ; so Llyn Cwellyn may be regarded as a relatively deep lake. It will be observed, 

 from an examination of the map (Plate V.), that the deeper part of the lake approaches 

 much nearer the lower than it does the upper end. The 120 feet depression has an 

 elongated form, is widest at its lower end, and tapers to a narrow channel as traced 

 upwards.. It corresponds to only 2*3 per cent, of the total superficial area of the lake. 

 The 110. feet depression is over half a mile in length, and is of a considerable extent. 

 It is broadest down lake, and tapers up lake obliquely towards the Mynydd Mawr shore. 





