444 • MR T. J. JEHTJ ON 



was 48 feet ; this was found in three places close to each other, about a quarter of the 

 way clown the lake from the head. The mean depth is 21 '3 feet, being 44 per cent, of 

 the maximum depth. The total bulk of water contained in the lake is approximately 

 57 million cubic feet. Geirionydd is deepest in its upper half. 



The area enclosed within the 40 feet subaqueous line lies a little nearer to the left 

 margin than it does to the. right. It is club-shaped in form, with the broad end up 

 lake, and the narrow end terminating about mid-way from both ends near the middle 

 of the lake. This area corresponds to 97 per cent, of the total superficial area of 

 the lake. The area enclosed within the 30 feet contour-line has a length of about 650 

 yards, and in all encloses 27 "8 per cent, of the total area. It does not extend as far 

 down as the bay which occurs on the western shore. The area within the 20 feet 

 line has a length of about 1000 yards, and extends to within 200 yards of the foot of 

 the lake. This contour-line is unaffected by the bay on the west side. Over half of 

 the total area of the lake lies within this line. 



The 10 feet contour-line keeps close to the shore-line along the right and left 

 banks, and follows the curve of the shore-line at the bay ; it extends to within 100 

 yards of the two ends of the lake. The area between the shore and the 10 feet line is 

 estimated to be 23 "8 of the total superficial area. 



An examination of the map and sections (Plates VI. and VIII.) will show that 

 opposite the deepest part the slope of the lake-bottom is steeper from the western shore 

 than it is from the eastern. But in the lower reaches, opposite the bay, the steepest 

 slope is from the eastern bank. The hollow in which Geirionydd lies is trough-like, 

 with somewhat steep sides and an approximately flat bottom. 



15. Llyn Cawlyd. — This is the largest of the numerous lakes situated in that 

 mountainous district lying between Bangor, Capel Curig and Conway, and it is the 

 deepest of all the lakes dealt with in this paper. Its upper end is about two miles due 

 north of Capel Curig, and the lake, which is over a mile and a half in length, trends 

 from south-west to north-east, and drains into the valley of the Conway. Cawlyd lies 

 almost parallel with Geirionydd and Crafnant, but is situated at a much higher eleva- 

 tion, being considerably over 1000 feet above sea-level. The lake is situated at the 

 head of a long narrow valley, and the mountains rise steeply from both banks to heights 

 of over 2000 feet. The slope of the hill on the right or southern side is very steep, 

 and along a great part of its length it is flanked by screes. On the right or northern side 

 the slope is not quite so steep, and about half-way down the lake, the hills fall back 

 a little, leaving a band of more gently rising ground immediately bordering the lake at 

 the lower end. The hollow in which the lake lies, ends abruptly at the upper end, the 

 ground rising fairly rapidty to the watershed, which is only about 300 feet above the 

 level of the lake. Cawlyd is ver) T narrow at its upper end, broadens a little towards 

 the middle, but narrows somewhat again towards the outlet. The shore-line on both 

 sides is very regular, there being no marked promontories or bays. There is no alluvial 

 tract in this case stretching upwards from the head of the lake. Cawlyd is remark- 



