446 MR T. J. JEHU ON 



rising more rapidly towards the lower end of the lake until the 40 feet line is reached, 

 after which the slope becomes gentle. 



At the sides the isobaths follow each other rapidly, and the slope is very steep from 

 both banks. 



Representative sections of Cawlyd are given (Plate VIII.). The longitudinal section 

 is along the axis of maximum depth. E-F is a section across the middle of the lake, 

 C-D towards the upper end, and G-H towards the lower end. At the upper end 

 the slope is steeper from the right bank ; at the lower end it is steeper from the left 

 bank. 



16. Llyn Dulyn. — This lake is situated in the heart of the wild and mountainous 

 district of Carnarvonshire, lying to the north-east of Nant Francon. Being very 

 difficult of access, it is but rarely visited. Its dark and gloomy waters lie in a deep 

 basin-shaped hollow, near the south-eastern base of Y Foel Fras, a mountain 

 attaining a height of over 3000 feet. Just to the south-west of Llyn Dulyn 

 the bare and rounded top of Carnedd Llewelyn is seen rising to a height of 

 3482 feet, which almost rivals that of Snowdon. Bare rock bounds the lake on all 

 sides except the east ; here a steep grassy slope rises, largely covered with boulders, 

 but this appears to be merely due to a thin covering of drift, and the rock probably 

 lies not far from the surface. On the western side the precipice is remarkable, the 

 rocky face coming down into the water, almost perpendicularly, from a height of several 

 hundred feet. Sheep often fall down this precipice, and a shepherd told the writer 

 that he had counted as many as twenty dead bodies at one time. Several tiny stream- 

 lets come trickling down the mountain-sides into the lake, which drains into the valley 

 of the Conway by means of Yr Afon Dutyn. This stream escapes at the south-eastern 

 corner, flowing out over rock. Just at this corner there is a small bay, which is, how- 

 ever, shallow. 



Llyn Dulyn is one of the highest mountain tarns in Wales, its surface lying, accord- 

 ing to the Ordnance Survey (April 1900), 1747 "2 feet above sea-level. It has a total 

 length of 560 yards, with a maximum width of 380 yards. The mean breadth is 297 

 yards, being 53 per cent, of the length. The waters cover an area of about 166,520 

 square yards. The survey of this lake was carried out in July 1901 under fairly favour- 

 able conditions. The total number of soundings taken was 94. The lake proved to be 

 remarkably deep, a depth of 189 feet being attained in one place. The mean depth 

 is very great, being as much as 104 '2 feet ; this is 55 per cent, of the maximum 

 depth. The bulk of water contained in the lake is estimated to be. about 156 million 

 cubic feet. 



An examination of the map (Plate VI.) will show that the deepest area lies approxi- 

 mately in the middle of the lake. This area is enclosed within the 180 feet line, and 

 corresponds to 10 per cent, of the total superficial area of the lake. The 160 feet 

 subaqueous line encloses a somewhat heart-shaped area, with its broadest part towards 

 the north ; towards the west the left corner of the broad end approaches very near to the 





