18 J. R. Dal-yns— Modern Denudation in iV. Wales. 



III. — Modern Denvdation in Xortu Wales. 

 By J. E. Dakyns. 

 rpHE subject of denudation is so important that I propose Kiving 

 X a few instances of denudation and of the transport of material 

 that have actually come under my own observation or that of my 

 friends. Where one sees the same famih'ar crags and pinnacles year 

 after year, apparently quite unchanged, one may perchance fancy 

 that denudation is at a standstill ; but anyone who, in scrambling 

 across the screes that clothe many a steep hillside, finds them moving 

 beneath his feet, or perhaps has clattering about his ears a shower of 

 stones dislodged by some wandering sheep, will at once perceive 

 that it is not so: for it is obvious that if the mere tread of such 

 a small beast as a sheep, shepherd or other pedestrian, can set scree 

 rolling downhill, it must be in a very unstable state, and may be 

 expected to move in a conspicuous manner under more potent forces 

 than the tread of animals. Observation shows that this is the case. 

 Not a year passes without some conspicuous fall of scree or of solid 

 rock, owing chiefly to great downpours of rain. Leaving general 

 statements, I will now give actual instances of the fall of rock or 

 movement of scree that have recently taken place in the Snowdon 

 district. 



In the Summer of 1897 a large mass of earth and rock debris was 

 ■washed by heavy rain down the hillside overlooking the east end of 

 Llyn Llj^daw, leaving a conspicuous scar which is still quite distinct. 

 A similar scar close by, which is actually marked on the Ordnance 

 six-inch map, was doubtless formed in a similar manner. Later on, 

 in August, under another downpour of rain, a similar scar was 

 formed on the Glyder near the head of Llanberis Pass. 



In June, 1898, after a great deal of wet weather, while the 

 summits were still enveloped in mist, I was scrambling along the 

 slope of Lliwedd, above Cwm Llan, when I was startled at hearing 

 from the side of Snowdon a noise like that of an explosion, followed 

 by the sound of falling rocks. Turning quickly round, I saw issuing 

 from the mist a quantity of earth and stones rushing down the 

 mountain-side, and leaving long trails ploughed out of the loose 

 material clothing the steep slope. Going up next day I found that 

 a large mass of rock, weighing several hundred tons, had slipped 

 down the hillside. The landslip was evidently due to a tiny rill 

 having been swollen by the recent rains and having washed away 

 some material supporting the highly weathered rocks, whose points 

 ■of support then gave way with snaps like explosions of gunpowder. 

 I once saw a somewhat similar fall of rocks in Norway caused by 

 a thunder-shower. In August, 1899, during heavy rain, a long 

 conspicuous scar was formed in scree on the side of Yr Aran. On 

 November 3rd, the day of the great gale, when from fifteen 

 to twenty streams were tearing down the mountain-sides, where 

 usually there are only two or three, the high-level footpath to 

 Snowdon was in three places either completely washed away or 

 •obliterated by being overwhelmed with stuff washed down the side 



