B. Mackintosh — Age of Floating Ice. 19 



their sources being probably the higher valleys of the Lake District 

 at a time when the N.W. of England and Wales was deeply sub- 

 merged. The greater part of the drifts, as may be inferred from the 

 height above the present sea of the sources of their stony contents, 

 must have been accumulated under water too shallow to float large 

 icebergs. Coast-ice, by freezing round and uprooting stones, debris, 

 clay and sand, and likewise by receiving loads of detritus from cliffs 

 and slopes, must be capable of removing much more drift-matter 

 than those icebergs which are the broken-off ends of high level 

 glaciers ; but while icebergs alone could have been sufficiently 

 powerfrd to uniformly grind down and niammilate large rocky pro- 

 jections, the comparative j)aucity of foreign drift (it is not altogether 

 absent) around these mammilated rocks in Anglesey may thus be 

 easily explained. There is no difficulty in accounting for the pre- 

 servation of the mammilated form during the rise of the land through 

 the upper part of the tidal range, for these rock-surfaces may have 

 remained covered with drift until just before their final emergence, 

 or they may never have been covered, and yet they may have risen 

 above the sea with their general form uneffaced, for we know that 

 at the present day glaciated rocks stretching from above to beneath 

 the sea on the coasts of Ireland, Scotland, and Norway, have resisted 

 the action of the waves for years ; and I am familiar with what some 

 years ago was a highly polished limestone surface on the W. coast 

 of Morecambe Bay, and which, notwithstanding its subjection to the 

 action of waves wielding pebbles, is still so smooth that care is neces- 

 sary in attempting to walk over it, while some of the striae can still 

 be dimly discovered. A short distance E. of the Monument there is 

 a well-preserved rocJie moutonnee, which has been glaciated up-hill 

 from about the N.E. The large shallow grooves may still be detected 

 under favourable light and shade, and the much larger parallel 

 undulations are very well defined (see Eig. 3). 



Fig. 3. — Boche moutonnee in Anglesey, looking leeward or down-stream. 



Nortliern Drift on Moel-y-Tryfan. — On the celebrated Moel-j^- 

 Tryfan, five miles S.E. of Caernarvon,' mixed local and northern 

 drift may be found. In the 35 feet of irregularly -stratified gravel 

 and sand which rises from the floor of the highest excavation of the 

 Alexandra slate quariy to within a few yards of the rock-crested 

 summit of the hill, there are some large felspathic and porphyritic 



^ Not the stupendous break-neck wedge of felstone, called Y Tryfan, at the head 

 of Nant Fran con, from going to which, in search of sea-shells, I lately prevented an 

 eminent savant. 



