478 On the question as to forma' Glaciers in North Wales. 



that it was not necessary to call in the aid of glaciers. The 

 spot is well known to tourists as one of the wildest and most 

 alpine in North Wales, where the torrents from Llyn Ogwen 

 and Llyn Idwal, on issuing from their respective lakes, are 

 precipitated over the rocky barrier that forms the head of 

 Nant Francon. Standing on the bridge between these two 

 torrents, the rocks on both sides, that form, as it were, the 

 crest of this barrier, and obstruct the free passage of the water, 

 seem to have a smooth or rounded form that is evidently not 

 natural. That in the stream of the Ogwen is the largest and 

 the most regularly domed ; and the side next the bridge 

 having been recently cut away in the direction of the cleavage, 

 their planes form a perpendicular face, on which the true lines 

 of stratification may be traced with sufficient distinctness. 

 The dip is towards the S.E. at an angle of about 40°, thus 

 proving the rounded top to have no connexion with either of 

 the divisional planes just named, or with the intersecting 

 joints, which, as usual, have flat surfaces. Though rounded, 

 the surface is not polished, but has a dull and weathered ap- 

 pearance, the effect of abrasion rather than of friction, on the 

 hard hornstone porphyry, of which the rock is composed.* 

 These rounded bosses of rock are at present some feet higher 

 than the level of the respective torrents that wash their bases; 

 but it is not difficult to believe that a period has existed when 

 they were covered by the torrent, and that in the lapse of 

 ages, the stones and ice it has carried along with it, having 

 given them this rounded form, have continually deepened the 

 channel, till the domed surfaces have been left projecting in 

 their present situation. 



Such are the principal appearances I have observed in 

 North Wales, which approximate to the effects produced by 

 existing glaciers upon the rocks and debris by which they are 

 surrounded. The phaenomena of moraines interested me 

 much in Switzerland ; and the recollections of their singular 

 features would, I think, have enabled me to detect any traces 

 of similar remains in the mountainous district under consi- 

 deration. I would not, however, be understood as meaning 

 to deny their existence in it altogether ; for there are still so 

 many obscure valleys that I have not visited, at least since the 

 discovery of the remains of glaciers in Britain, that it would 

 be presumptuous to speak dogmatically upon so obscure a 

 subject. My object has been to confine myself to what I have 



* Several varieties of hornstone porphyry are seen near this spot ; and 

 on the ascent toCwm Idwal a thick perpendicular vein of hornstone schist 

 is exposed, and is thrown by a dislocation on the opposite side oi the road 

 west of the bridge. It is extracted for whetstones. 



