58 J. E. Marr and R. H. Adie — The Lal;es of Snon-don. 



lias merely rounded off the edges of the escarpments without altering 

 their genei'al character. It has acted like sandpaper, and there is no 

 indication of such erosion as would j^roduce a rock-basin, — quite the 

 reverse. The same feature may be noticed in the case of Sprinkling 

 Tarn on Scawfell. 



The last cwm which contains lakes is the magnificent one east 

 of the summit of Snowdon. The lowest lake, Llyn Teyrn, is 

 shallow, and the stream from it flows over drift for a long distance 

 below the exit. Near this tarn, and close to the path, a glaciated 

 rock shows intercrossing strige, one set running east and west and 

 the other about 30° E. of N. and 30° W. of S. A better example of 

 intercrossing is seen by the path bordering the shores of Llyn 

 Llydaw, due west of the causeway. A roche montonnee shows three 

 sets of striations — one trending E. and W., another S.W. and N.E., 

 and the third 35° W. of N. and E. of S. Tliese directions point 

 respectively to the top of Snowdon, the Lliwedd cliffs, and the cliffs 

 immediately above the roclie moutonnee, and were probably produced 

 by glaciers coming from tliose directions at different times. We call 

 attention to them to emphasize a difficulty which has often been felt 

 if one assumes that glaciers can carve out rock-basins and yet are 

 unable to obliterate the strias formed at other times. Mr. Kendall 

 has, however, shown that the same mass of ice produces intercrossing 

 strise ; also, we are aware that glaciers, like rivers, must be under 

 conditions more favourable for erosion at some times than at others ; 

 the difficulty is, therefore, by no means insuperable to those who 

 maintain the power of ice to form rock-basins, but still we think it 

 is a difficulty. 



Mr. Watts writes: — "Immense quantities of moraine material 

 occur on the south-east side of Llydaw, but a careful examination of 

 the map shows that only two possible outlets exist — that now used 

 for the purpose ; and a second which is occupied by bog resting 

 on moraine, and gives rise to a small stream which is joined lower 

 down bj' the outlet of Llyn Teyrn. The moraine is, however, only 

 a thin skin on the surface of the rock. The present outlet shows 

 live rock forty or fifty feet below the level of the lake, and the 

 second possible exit at a rather less distance below the same level. 

 If the moraine were stripped off, there is little doubt that this 

 lake .... would show a basin of rock which would hold 

 water, unless it is very much shallower than is generally supposed to 

 be the case." It is very desirable that accurate soundings of this 

 lake should be made ; indeed, we wish someone would do for the lakes 

 of North Wales what Dr. Mill has so admirably performed in the 

 case of those of English Lakeland. Mr. Watts' observations would 

 permit the existence of a lake forty feet deep, which is not situated 

 in a rock-basin, and our observations lead us to believe that a very 

 much greater depth of water may be here held up by drift. A great 

 moraine runs right across Llyn Llydaw near the present outlet. It 

 is seen rising into high hillocks on the north side of the lake, 

 projecting as islets from the lake itself, and covering much ground 

 on the south side below the exit. No doubt it is, as Mr. Watts says, 



