424 MR T. J. JEHU ON 



mass of Snowdon, with its many peaks and buttresses, stands isolated from all others. 

 It is bounded on three sides by valleys : on the north-east lies the narrow pass of 

 Llanberis, at the lower end of which are situated the two lakes Padarn and Peris ; on 

 the south-east the deep Vale of Gwynant, with its two lakes Llyn Gwynant and Llyn-y- 

 Ddinas ; the boundary to the south-west is formed by Nant Colwyn and the Gwyrfai 

 Valley, the latter of which holds the lakes of Llyn-y-Gader and Cwellyn. The highest 

 peak of Snowdon- — Y Wyddfa — towers to a height of 3560 feet above sea-level. 

 Standing on the summit we can see that Snowdon is penetrated on all sides by wild 

 upland-valleys or cwms. These vast hollows are six in number, and many of them 

 harbour lakes. They are tributary to the bigger valleys below ; Cwm-glas-bach and 

 Cwm Glas, opening north-eastwards on to the Pass ; Cwm Dyli and Cwm-y-Llan, south- 

 eastwards on to the Vale of Gwynant; Cwm-y-Clogwyn, westwards above the Vale of 

 Gwyrfai ; and Cwm Brwynog, towards the north. Soundings have been taken of two 

 of the lakes, Llyn Llydaw and Llyn Glaslyn, lying in Cwm Dyli. 



To the north-east of the Pass of Llanberis is another mountain mass, comprising 

 several heights. The Glyders, y Tryfan, y Garn, and Elidyr Fawr, all rise to heights 

 of over 3000 feet; and Y Foel Goch, Moel Perfedd, and Elidyr Fach, exceed 2500 feet. 

 This area is bounded on the south-east by Nant-y-Gwrhyd, at the lower end of which 

 are the lakes of Capel Curig, and on the north-east by Nant Francon and Nant-y-Ben- 

 glog, at the head of which is situated Llyn Ogwen. The bottom of Nant Francon, for 

 some miles below the head, probably marks the site of an old lake. A great number of 

 cwms or corries open eastwards out to Nant Francon and Nant-y-Benglog, and in one of 

 these, above the top of the Pass, lies Llyn Idwal. 



To the north-east of the Nant Francon and Nant-y-Benglog depression, is situated 

 the third and largest mountain tract. It is bounded on the south by the Vale of 

 Llugwy, and on the east by the Vale of Conway. This tract presents a very rugged 

 and wild aspect. It includes several high mountains, the most noteworthy of which 

 are Carnedd Dafydd, Carnedd Llewelyn, and Y Foel Fras, all rising to heights of over 

 3000 feet. This tract is very rich in lakes, many of which occur at a very high alti- 

 tude. The larger ones are described in this memoir, and include Dulyn, Eigiau, Cawlyd, 

 Crafnant, and Geirionydd. Dulyn is a corrie-lake. The others lie in valleys, some of 

 which have cirque-like heads. They all drain north-eastwards into the Vale of 

 Conway. 



IV. Methods. 



The methods of carrying on the work were similar to those employed by Dr Mill in 

 his survey of the English lakes. All the soundings were taken from rowing-boats, 

 which on most of the lakes were hired without difficulty. But on some of the lakes 

 lying at high elevations, no boat was to be found ; in such a case arrangements had to 

 be made for the conveyance to the lake of a boat from the nearest place where it was 

 possible to get one. This often proved to be no easy matter, for some of the lakes are 



