THE LAKES OF SNOWDONIA AND EASTERN CARNARVONSHIRE. 435 



to south-west. Much of the valley between the two lakes is occupied by drift, through 

 which the river is gradually cutting its way. The valley broadens at some distance 

 above the lake, and the river Glaslyn here flows over low ground, and enters the lake 

 at the apex of a large delta. The lake is broadest in its upper half, and narrows as 

 we approach its lower end. It is not as long as Gwynant, its exact length being 

 1240 yards. Its maximum width is 420 yards, and it covers an area of about 371,920 

 square yards. The mean breadth is 300 yards, and this is 24 per cent, of the length. 

 Several tributary streamlets join the lake from the left side, the largest of which is the 

 Afon Goch, entering near its foot. The shore-line is, on the whole, very even, the 

 only irregularities worth noticing being those formed by the delta at the head, and a 

 small grassy promontory jutting into the lake from the left side, opposite the middle of 

 the lake. 



The hills rise steeply on the Snowdon side to a height of over 1000 feet. On the 

 -opposite side the coast is flatter for some distance from the head, after which the hill- 

 sides again rise steeply. Near the end of the lake the valley becomes more contracted, 

 -and the water flows out by a weir through a narrow strait between rocky hills. The 

 upper part of the lake is very shallow, and water-plants advance into the lake for a long 

 distance from its upper left hand corner. It is evident that the lake is being gradually 

 -silted up towards its head. 



In the work on Llyn Dinas I had again the assistance of Mr Philip Lake. The total 

 number of soundings taken was 61. A bench-mark being found near the lake-margin, 

 we were able, by means of an Abney's level, to ascertain the elevation of the water- 

 surface to be 175"45 feet, as against 175*9 feet obtained by the Ordnance Survey in 

 June 1886. 



Llyn Dinas is a shallow lake, the greatest depth recorded being only 30 feet. The 

 ■small area attaining this depth lies near the middle of the lake. The mean depth is but 

 12*9 feet ; this is 43 per cent, of the maximum depth. The bulk of water in the lake is 

 -calculated to be about 43 million cubic feet. A glance at the map (Plate V.) will 

 show that the configuration of the lake-bottom is very simple. A large proportion of 

 the upper half of the lake is under 10 feet in depth. The deeper areas extend more 

 into the lower half, and have a somewhat oval shape. Of the total superficial area as 

 much as 48*8 per cent, corresponds to depths under 10 feet, and only 27 '6 per cent, 

 -corresponds to depths of over 20 feet. 



The longitudinal section given (Plate VIII.) shows that most of the water lies in 

 •the lower two-thirds of the lake, the upper third being very shallow. The slope is 

 gentle from both sides, and the cross-sections C-D, E-F, give pan-shaped figures. The 

 lake-bottom was very muddy, and often the lead was only pulled out with difficulty. 

 The lake is, in all probability, getting silted up rather rapidly. 



9. Llyn Cwellyn. — Snowdon is bounded on the west by the Gwyrfai Valley. Near 

 the head of this valley lies a small and shallow lake bearing the name of Llyn-y-Gader. 

 The river Gwyrfai issues from this lake and runs in a northerly direction, to lose itself 

 TRANS. ROY. SOC. EDIN., VOL. XL. PART II. (NO. 20). 3 v 



