Edivard Greenly — Glaciation of Holyhead Mountain. 505 



The whole mountain is strongly rubbed and moutonnee on the 

 north-east side, every boss having the characteristic outline. (The 

 outline of the vi'hole mass, indeed, is like that of a gigantic roche 

 moutonnee.) On many of these surfaces, which are often polished 

 and shine in the sun, the hard and enduring quartzite still retains 

 fine striae, while towards sunset on a summer's evening they can 

 be detected almost everywhere. The rocks of the South Stack 

 series have not retained them so well. The general direction is 

 N.E.-S. W., with local variations and deflections ranging from S. 35° W. 

 to W. 40° S. A more marked deflection is S. 10° W. near the flag- 

 staff above the South Stack. On the South Stack itself they run 

 S.S.W., fanning out to south-west on the slope of the boss. Along 

 the southern slopes of the mountain they tend to west of south-west. 



Striae cross the summit itself running S. 40° W. The ridge at the 

 summit and towards the North Stack falls steeply westward for 50 or 

 100 feet before breaking into the crag and sea-cliff alluded to above, 

 and at the brow of this vertical cliff the rocks are still polished and 

 traversed by striiB running in the usual N.E.-S.W. direction, in spite 

 of being under the lee of some 50 or 100 feet of steep rock. 



Undercut furrows have not been observed on the mountain itself, 

 but it may be worth while to note that they occur at Ffynnon 

 Gorlas, on the lower ground at its eastern foot, where, also, a surface 

 facing south-west and overhanging, as much as 40°, and in one place 

 60°, from vertical, is rubbed and smoothed. 



The mountain proper (excluding the South Stack moors) is very 

 bare of drift, but a little till occurs in the hollows, with debris^ 

 chiefly from the eastward so far as yet recognized. Many large 

 boulders of the quartzite occur on the South Stack moors. 



At the summit are many small fragments of the well-known green 

 mica-schists of the neighbourhood of the town, with other erratics. 

 These schists do not occur in situ at a greater elevation than about 

 220 feet ; and in the direction from which the strise indicate ice- 

 movement, not more than 100 feet. The fragments have therefore 

 been lifted 500 feet at least, and almost certainly 600 feet, during 

 their journey. 



Although it has long appeared to me that we have much, to 

 learn from research in Arctic and Antarctic lands, and cannot hope 

 yet to be able to explain many of the glacial phenomena of the past, 

 yet a group of facts like these of Holyhead seem to be more easily 

 explained by the passage of land-ice than by any other hypothesis. 



The general direction of glaciation, it may be observed, is parallel 

 to that of the mainland of Anglesey so far as I have yet examined it. 



In conclusion, there are some banks and mounds on both sides^ 

 of the mountain, the most marked being on the south-west side, 

 which have much of the appearance of moraines ; and are, moreover, 

 so far as I can make out, composed almost exclusively of quartzite 

 debris. It would be interesting if, in spite of the comparatively 

 slight elevation, one or two small local glaciers had lingered, or 

 perhaps for a short time formed, upon this exposed and lonely hill. 



