406 W. A. Brend — Lakes of Caernarvonshire. 



of the exit stream rock in situ can be detected along the footpath, 

 but between this and the stream is an area of which, though it does 

 not look like a drift- filled depression, it is not possible to speak with 

 certainty. It is flat and marshy, and though drift is not visible 

 neither is rock. The narrowest point is about 10 feet below the 

 level of the lake ; a drift dam here, then, must be 40 feet thick, as 

 the maximum depth of the lake is 50 feet. It may be pointed out 

 that the shape of the western margin of Llyn Geirionydd renders 

 any explanation of its formation by glacial erosion difficult to 

 accept. 



About three-quarters of a mile to the west on the other side 

 of Mynydd Deulyn is Llyn Crafnant, situated 602 feet above 

 sea-level. The stream, . which drains the lake, flows out through 

 a gorge about 100 yards long : on the. left bank a cliff rises nearly 

 vertically for about 40 feet, and then slopes back ; on the right bank 

 is a path about 3 yards wide, and then a steep rocky declivity. 

 Eock in situ occurs below the path at intervals along the margin of 

 the stream. The actual bed of the stream is filled with large 

 boulders, and it is impossible to trace rock across it. The narrowest 

 place is a point about 10 feet below the level of the surface of the 

 lake ; here the rock- walls of the stream are 17 yards apart ; in other 

 places the distance between them varies from 20 to 30 yards. If 

 the loose material seen in the bed of the stream really dams up the 

 lake, it must descend to a very considerable depth, as the writer 

 obtained several soundings over 70 feet, and Mr. Kingsley, who 

 sounded the lake some years ago for the Ordnance Survey, found 

 90 feet in one place. As the fall through the gorge is considerable, 

 and the stream pretty strong, it does not seem probable that the 

 loose material can be of any great thickness. 



Considerable attention has been paid to the description of the exit 

 of Llyn Crafnant, as there seems to be no other place where the lake 

 is likely to have been dammed. Bare and rugged mountains rise up 

 continuously all round the lake, in one place only below 1,000 feet 

 high. This is a narrow depression through which the path from 

 Llyn Geirionydd runs ; the highest point is about 360 feet above the 

 surface of the lake. Here the interval across which rock cannot 

 be traced is about 25 yards wide ; 200 yards south-east of this 

 the width is reduced to less than 20 yards. If this depression 

 represents a drift-filled valley damming the lake, it is at its highest 

 part from 60 to 80 feet wide for about 200 yards and at least 

 430 feet deep. The existence of such a rift as this seems highly 

 improbable. 



The lake is shallow at the narrow end, and shelves down 

 gradually to about 30 feet just beyond the first tributary stream ; 

 from this point it shallows to about 15 feet opposite the next 

 tributary. From here it deepens rapidly to about 70 feet near the 

 Centre of the lake. A depth of between 50 and 70 feet is main- 

 tained for some distance, and then it rapidly shallows up to the 

 alluvial flat. 



A largo lake, Llyn Cawlyd, about a mile to the north-west of 



