T^ Mr Murchison on the Glacial Theory. 



rently formed sets of parallel markings which he obsen'cd iti the newly 

 uncovered surfaces of tlie schistose Silurian rocks, and shews satisfao- 

 torily how such appearances, as well as the tops of the joints, might be 

 mistaken by cursory observers for scratches, although they are in fact due 

 to structure. 



Unlike Mr Bowman, Dr Buckland has not confined his views of the 

 action of glaciers to Scotland, but applies them largely to the north of 

 England and to Wales. He has recently endeavoured to satisfy us, that 

 the rocks on the sides of the chief valleys in the latter country which 

 open out from a common centre of elevation are striated, worn, and po- 

 lished in the direction of the present water-courses, and these he con- 

 ceives to be evidences of former glaciers, which filled up all the valleys 

 radiating from Snowdon to a distance of many miles from a common 

 centre. I confess I see almost insurmountable objections to this view. 

 Apart from other evidence, the very physical geography of this tract is 

 at variance with the construction of such an hypothesis. In the Alps, 

 aiid indeed in every other part of the world in which they have been ob- 

 served, the length of glaciers is in ratio to the height of the mountains 

 from which they advance, or, to use the words of Agassiz, from which 

 they earpand. Now, whilst in the present days, a small glacier hangs to 

 the sides of a mighty giant like Mont Blanc, having the altitude of 16,000 

 feet, our Welsh hills, having a height only of 4000 feet, had glaciers, by 

 the shewing of Dr Buckland, of a length of many miles. Again, in tlie 

 same memoir, which fills so large a portion of the principality with gla- 

 ciers, the author comments upon certain facts already well known to us, 

 viz. the existence upon Moel Tryfane and the adjacent Welsh moun- 

 tains of sea-shells of existing species, at heights of 1500 and 1700 feet 

 above the sea, where they are associated w^ith mixed detritus of rocks 

 transported from afar, all of which have travelled from the north, the 

 hard chalk and flints of the north of Ireland being included. How are 

 we to reconcile these facts with the theory that the greater part of the 

 country in question was frozen up under the atmosphere in some parts of 

 the same modern period? Unable otherwise to explain how marine 

 ' shells should be found on mountains which are supposed to have been 

 previously and during the same great period occupied \>y terrestrial gla- 

 ciers the accumulation of ages, Dr Buckland invokes anew the aid of the 

 old hypothesis of a great wave. This wave, rolling from the north, must 

 have dashed over the mountains to a height of near 2000 feet, depositing, 

 as it went, gravel, boulders and fragments, derived from places 200 miles 

 distant, and transporting also marine shells in its passage. But is it not 

 more natural and accordant with all the data upon which our science has 

 been reared, to suppose that when such shells were deposited, the parts ^ 

 of the mountain so afiected were permanently beneath the sea, than to f 

 call into play the assumptiou of the passage of so mighty a wave .'' A<?' 

 one moment the argument used is, that scratchings and polishings *^ 

 rock must hare been done by ice, because in existing nature it ha9 b 



