428 MR T. J. JEHU ON 



shore-line, and the slope to the bottom is very steep from the head of the lake and from 

 the sides, as shown by the sections given on Plate VIII. 



3. Glaslyn, the highest of the lakes of Snowdon, lies at an altitude of nearly 2000 

 feet above the level of the sea. The old and correct name is Ffynon Las (The Green 

 Well), so called on account of the bluish-green colour of its waters. 



The lake lies east and west, and is encircled on three sides by precipitous rocks. On 

 the west it is surmounted by the great precipice of Y Wyddfa, which has an almost 

 sheer fall from the top of Snowdon to the head of the lake ; on the north it is bounded 

 by Crib-y-Ddysgyl and Crib Goch, and on the south and south-east by Y Crimau and 

 the ridge of Y Gribbin. The outlet is towards the east, whence a streamlet issues and 

 rushes down a steep rocky slope to make its way below to Llyn Llydaw. The lake is 

 considerably longer than it is broad, and its margins are very regular, with the exception 

 that it is indented by a bay on the north side, and that it narrows towards the exit on 

 the east. The path from Penygwryd to the summit of Snowdon follows the northern 

 side of the lake. A streamlet flows in at its north-east corner, and its point of entrance 

 has, owing to rock-rubbish carried down from the copper-workings above, been shifted 

 down lake a little since the preparation of the Ordnance Survey map. 



The soundings on Glaslyn were made on 24th August 1900, under most favourable 

 conditions, the weather being beautifully calm, and not a ripple disturbing the surface 

 of the waters. The soundings were all taken by myself, and the rowing done by an excel- 

 lent boatman. We were able to steer perfectly straight courses from side to side, and 

 so the work done on this lake was more accurate and complete than that done on any 

 other of the lakes of this group. Situated high up in one of the deepest recesses of 

 Snowdon, the surface of this gloomy lake is, according to the Ordnance Survey maps, 

 1970'7 feet above the sea-level. It has a total length of 535 yards, with a maxi- 

 mum breadth of 275 yards, Its mean breadth is 197 yards, being about 37 per cent, 

 of the length. Its waters cover an area of about 105,600 square yards. The number 

 of soundings taken in Glaslyn was 107. The greatest depth registered was 127 feet, 

 and this is approximately in the centre of the lake. The mean depth has been calculated 

 to be 62 - 6 feet, and this is 49 per cent, of the maximum depth. The bulk of water 

 contained in the lake is estimated at 59,500,000 cubic feet. 



An examination of the map (Plate IV ) shows that the lake is deepest in the middle, 

 and that the contour-lines follow each other with great regularity. The relation between 

 the length and the breadth of the area enclosed within each contour-line is very similar 

 to that of the length and breadth of the la^e as a whole. The bay on the northern side 

 causes the 20 feet contour-line to curve outwards more or less parallel to the shore-line, 

 and the 40 feet and 60 feet contour-lines to curve out to a less extent. The contour- 

 lines marking greater depths are unaffected by the bay. There is a curious curving 

 inwards of the contour-lines from a point on the southern shore ; all the lines are 

 affected in a similar way, but the indentation is especially marked on the 120 feet 

 contour-line. The cause of this is not obvious ; but it may be noted that just at this 





