460 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



April 16. 1845. 



On the supposed Evidences of the former Existence of Glaciers 

 in North Wales. By Angus Friend Macintosh, Esq., 

 F.G.S. 



The author states, that having noticed some remarkable pheno- 

 mena in a part of North Wales, which seemed to militate strongly 

 against the theory advanced by Prof. Agassiz, and supported by 

 Dr. Buckland, on the subject of glaciers, he was induced to ex- 

 amine carefully the district in question, and that, after long inves- 

 tigation, he has formed a decided opinion that the district affords 

 no sufficient proof of the former existence of glaciers in any part 

 of it. He then considers seriatim the different points of evidence 

 that have been adduced and their value. 



1 . Rounded Surfaces of Rock. — These appearances, which have 

 been referred to by Dr. Buckland as having been caused by 

 glacial action, abound in several of the Welsh valleys, in some in- 

 stances (near Bedd-gelert and the pass of Llanberis) at the height 

 of 800 and 1000 feet, and in others at a very much more consider- 

 able elevation. If, however, it was by the agency of ice that such 

 rounded surfaces were produced, the valley must have been en- 

 tirely occupied by the glacier, which in some cases it would seem 

 must have had a thickness of at least 2500 feet. This indeed is 

 according to M. Agassiz' theory, that the ice extended downwards 

 to the plains, and covered the surface ; but the modified form of it 

 adopted by Dr. Buckland does not in the author's view account 

 for -the existence of the rounded masses, since they are promis- 

 cuously dispersed in some of the valleys, occurring in numerous 

 and very different directions, and often where no true glacier 

 could be supposed to have reached them. 



The want of height in the Snowdonian hills is adduced by the 

 author as an argument that such vast bodies of snow and ice could 

 not have been formed on them, since the length of glaciers is known 

 to be in the ratio of the height of the mountain whence they pro- 

 ceed ; and he further observes that the glacial theory with regard to 

 these rounded surfaces is also strongly opposed by appearances 

 which occur on both sides of the lower Llanberis lake on the old 

 Bangor road, near the south end of the Penrhyn quarries in the 

 valley of Nant Francon at its upper extremity, and in several other 

 places. Here the rounded surfaces are seen immediately in contact 

 with, and directly under cover of, other masses higher than them- 

 selves, these latter standing immediately before them in the line 

 of descent, and yet having their edges, over which the glacier 

 must have passed (if it rounded the rocks below), angular, and 



* Proc. Geol. Soc. vol. iii. p. 579. 



