1849.] MURCHISON ON THE DETRITUS OF THE ALPS. 07 



of "moraines" in that detritus of the larger valleys which has been 

 theoretically referred to old glacier action. 



In descending from the higher Alps into the main or trunk valleys. 

 Sir Roderick found many examples of rocks rounded on that side which 

 had been exposed to the passage of boulders and pebbles, with abrupt 

 faces on the side removed from the agent of denudation, all of them 

 reminding him forcibly of the storm and lee sides of the Swedish rocks 

 over which similar water-worn materials have passed. 



Seeing, then, that this coarse drift or water-worn detritus is dis- 

 tributed sometimes on the hard rocks and often on the remnants of 

 the old valley alluvia, he believes that the whole of the phsenomena 

 can be explained by supposing that the Alps, Jura, and all the sur- 

 rounding tracts have undergone great and unequal elevations since 

 the period of the formation of the earliest glaciers — elevations which, 

 dislodging vast portions of those bodies, floated away many huge 

 blocks in ice rafts, down straits then occupied by water, and also 

 hurled on vast turbid accumulations of boulders, sand and gravel. 

 To these operations he attributes the purging of the Alpine valleys 

 of the great mass of their ancient alluvia, and also the conversion of 

 glacier moraines into shingle and boulders. He denies that the 

 famous blocks of Monthey opposite Bex, can ever have been a portion 

 of the left lateral moraine of a glacier which occupied the whole of the 

 deep valley of the Rhine, — as Charpentier has endeavoured to show ; 

 and he contends that if such had been the case they would have been 

 associated with numberless smaller and larger fragments of all the 

 rocks which form the sides of the valley through which such glaciers 

 must have passed. They are, however, exclusively composed of the 

 granite of Mont Blanc ; and must therefore, he thinks, have been 

 transported by ice rafts, — which, having been forced mth great 

 violence through the gorge of St. Maurice, served to produce many 

 of the striae which are there so visible on the surface of the lime- 

 stone*. 



Fully admitting that the stones and sand of the moraines of 

 modern glaciers scratch, groove, and polish rocks. Sir Roderick 

 Murchison still adheres to the idea he has long entertained from 

 surveys in Northern Europe f, that other agents more or less sub- 

 aqueous, including icebergs and heavy masses of drift, have produced 

 precisely similar results. He cites examples in the Alps, where 

 perfectly water-worn or rounded gravel being removed, the subjacent 

 rocks are found to be striated in the directions in which such gravel 

 has been moved ; and he quotes a case in the gorge of the Tamina, 



* Mr. Charles Darwin, in a recent letter to the author, adheres to his old 

 opinions on this point, derived from observations in America, and says, " I feel 

 most entirely convinced that floating ice and glaciers produce effects so similar, that 

 at present there is, in many cases, no means of distinguishing which formerly was 

 the agent in scoring and polishing rocks. This difficulty of distinguishing the 

 two actions struck me much in the lower parts of the Welsh valleys." 



t See Silurian System, pp. .509 to 547 ; Russia in Europe and the Ural Moun- 

 tains, vol. i. pp. 507 to 559 ; Presidential Discourses, Proc. Geol. Soc. Lond. vol. iii. 

 p. 671, and vol. iv, p. 93 ; Journ. of Geol. Soc. Lond. vol. ii. p. 349 ; and Trans. 

 R. Geol. Soc. Cor. 1 wall, vol. vi. 



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