74 



PROF. T. M'KENNY HUGHES ON" THE 



Part II. 

 The Arenig Drift. 



Any one standing on Arenig or Llyfnant and looking round over 

 the wide expanse of unenclosed moorland, would see at a glance that 

 there, to the west, was a basin in which, under somewhat different 

 conditions, snow might collect to any depth and, compacted into ice, 

 crush its way out towards Bala between the two Arenigs and over 

 the col between Llyfnant and Arenig Mawr, towards the head of 

 Bala lake. There, to the north, was an area on which neves would 

 be formed of the snow that was blown from the crags of Snowdon 

 or Moel Siabod, or many another glorious peak. There is the 

 western sea stretching away beyond the mountains of Harlech, and 

 feeding with moisture the prevalent south-west wind, which keeps 

 the hill-sides for ever damp, and at Blaenau Ffestiniog, as I was 

 informed by Mr. J. H. Williams, throws down yearly 133 inches of 

 rain. The dark southern end of the valley west of Arenig still 

 holds the winter's snow in its deep shadow far through the summer, 

 and has in consequence the name of Twll-yr-eira, "the hole of 

 the snow." The long esgair-like ridges running down from it are 

 probably due to the torrents diverted by the snow. 



Push the mountains up till the moisture that fell should all fall 

 as snow, and the summer's sun should quite fail to undo the winter's 

 frost, then the neve must form there, and glacier-ice must flow 

 from the Arenigs and Siabod, from Snowdon and the Carneddau. 



But we are not left to mere speculation on this point. Over 

 the col and along the east slopes of Llyfnant the glacial striae are 

 still seen running south. They score the rock in long east and 

 west furrows on the rounded shoulders of Arenig Mawr above 

 Milltirgerig. 



Here and there, in some deep hollow, the remains of the old drift 

 is still seen, and a few scratched stones are found in the fine putty- 

 like felspathic mud worn as the flour of rock in and under the ice 

 from the volcanic ashes that there abound. An example of this 

 drift is seen in the hollow scooped out in the soft Graptolite-bearing 

 shale east of Maengrugog. 



Also we see whence the boulders came that lie scattered over 

 all the region to the east. Under every precipice of ash and various 

 porphyritic rock there is a talus formed of enormous blocks fallen 

 from the cliffs above. These are mostly well-marked rocks which 

 do not occur again in place among the formations further east. 



So we can trace this drift by its boulders and fine felspathic mud 

 and small variety of rock up to the valleys of the Dee and Clwyd 

 and far beyond. 



As we travel east the fragments from the rocks of Arenig and its 

 surrounding district become, of course, less conspicuous compared 

 with the' material that the ice has gathered on its way ; but all 

 the material has been transported from the west — all from the 

 rocks of Wales — and the striations on the solid rock agree with 

 this. We have already noticed how the grooves ran round the 



