J. R. D:(Iii/ns — Jlodeni Denudation in ^Y. Wales. 19 



of Crib y Dilysgl. A few days after this, on going to seek shelter 

 from rain in an ohi adit level, where I had often sheltered two 

 years ago, I found it completely covered with screes, which had 

 either come down in a similar manner previously or had gradually 

 accumulated during the last two years. Another old level, which 

 was open when I was a boy, has long since been quite covered by 

 scree. 



A long red scar is to be seen on the hillside between Lliwedd 

 a,nd Gait y Wenallt : this was formed in March some years ago by 

 an avalanche caused by the sudden melting of the winter's snow 

 under heavy rain. A friend of mine saw and heard it come down 

 with a roar like thunder. 



Another cause of the fall of rocks is liglitning. I often see 

 freshly broken rocks that look as if they must have been broken 

 by lightning : such a one I noticed the other day below Crib Goch, 

 which had probably been struck by lightning during the thunder- 

 storm that occurred on the 20th of July, 189i^ ; but it is not often 

 that we actually know as a fact that such and such a rock has been 

 struck by lightning. During the great thunderstorm that occurred 

 in North Wales in the middle of August, 1898, a mass of rock was 

 broken and thrown down near Llyn Teyrn. This is known to have 

 been done hy lightning, as it was not there till after the storm. It 

 is still quite distinct. 



It will thus be seen that scree is perpetually moving down to 

 a quite conspicuous extent under the influence of water, and that 

 large landslips and falls of rock are also caused by heavy rain and 

 by lightning. I have not had an opportunity of observing in 

 Wales the transport of stones by ordinary mountain torrents ; but 

 doubtless such torrents behave in Wales as similar streams do in 

 Yorkshire, about which I happen to know something. I once lived 

 at Kettlewell in Craven, in a room overlooking a mountain torrent. 

 I had not been there very long before there was a deal of heavy 

 rain; and one night, after all the village folk had gone to bed, 

 I heard a bumping noise as if a heavy cart were jolting over a rough 

 road ; so, being surprised that anyone should be driving a cart at 

 dead of night, I opened the window and looked out, and I then 

 discovered that the noise was caused by boulders bumping against 

 one another as they were swept down by the beck that flowed under 

 my window. Whenever there was heavy rain on the hills, that 

 bumping noise was heard. The beck, when in spate, which it often 

 was, invariably rolled great stones down to the river Wharfe. No 

 doubt mountain streams in Wales and in other hilly countries 

 do likewise. I may here remark that this transport of stones may 

 go on in clear water. In such a country as the volcanic parts of 

 ■Cumberland and Westmorland, where there is no shale, very little 

 peat, and all the rocks are hard, a stream, even when in spate, will 

 run quite clear, but it is hurrying stones on along its bottom all the 

 same. The effect of this may be seen in many places in the great 

 spreads of gravel that occur where a mountain stream enters a river 

 valley, as for instance where such a stream enters the valley of the 



