426 MR T. J. JEHU ON 



V. Description of the Individual Lakes and their Surroundings. 



The largest and most magnificent of the cwms of Snowdon — Cwm Dyli — penetrates 

 the mountain mass from the south-east. It has the form of a huge rocky amphitheatre, 

 bounded by the precipitous cliffs of Lliwedd, Y Wyddfa, Crib-y-Ddysgyl and Crib Goch. 

 Enclosed within this vast hollow are three lakes — Llyn Teyrn is the lowest, Llydaw lies 

 in the middle, and Glaslyn is the highest. 



1. Llyn Teyrn is a small tarn somewhat oval in outline, and lying at a height of 

 a little over 1200 feet above sea-level. It appears to be shallow, and the streamlet 

 draining the lake flows out over drift. 



2. Llyn Llydaw is a beautiful sheet of water rather more than a mile in length, lying 

 in the heart of this upland valley, and taking an oblique direction across it. The lake 

 has an irregular and somewhat winding outline ; the axis runs first from west to east, 

 then turns towards the north-east, and finally bends back again to the east. The water 

 of Llyn Llydaw is of a markedly green or light blue colour, and this is usually ascribed 

 here to the presence of copper, as mines for this mineral are worked close to the lake. 

 But according to Messrs Marr and Adie, not a trace of copper was found on analysis 

 either in the water of this lake or in that of Glaslyn. 



Only one important stream — the Afon Glaslyn — enters the lake ; it comes from the 

 tarn higher up the cwm, and flows into Llydaw at its north corner, bifurcating into 

 two branches a short distance above its junction with the lake. Other tiny streamlets 

 run into Llydaw on either side. During dry weather these are mere rills, but after 

 heavy rain they become temporarily swollen into rushing torrents, and carry much rock- 

 rubbish from the steeper slopes into the lake. The river Glaslyn flows out at a point 

 on the south-eastern shore about a third of the length from the lower end of the lake, 

 and runs south-eastwards, making its way eventually by a waterfall down to Nant 

 Gwynant. 



In its upper reaches the lake has a fairly regular outline, but lower down the shore- 

 line becomes more irregular, owing to the immense quantities of morainic material 

 scattered about, especially on the south-eastern side. The remains of a great moraine 

 can be traced near the outlet ; portions of it occur as islets, composed of boulders and 

 loose material, opposite the mouth of the stream ; a continuation of the same moraine 

 can be traced on the northern side opposite in the shape of huge mounds. 



A causeway crosses the lake at its narrowest part, and for the construction of this 

 the surface of the lake was, according to the late Sir Andrew Ramsay, lowered as much 

 as 1 6 feet. Beyond the causeway the lake widens out again considerably. 



The work done on Llydaw occupied the 2lst, 22nd, and 23rd of August 1900. The 

 weather conditions were, on the whole, favourable, but at times the wind was trouble- 

 some, making it difficult to steer straight courses from side to side, and during the last 

 day heavy showers made the work unpleasant. 



