the Superficial Detritus of the Alps, 525 



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

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

 the remnants of the old valley alluvia, he believes that the whole df 

 the phsenomena can be explained by supposing that the Alps, Jura, 

 and all the surrounding 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 down straits then occupied by water, and 

 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 with 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 limestone*. 

 Fully admitting that the stones and sand of the moraines of 

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

 Murchison still adheres to the idea he has long entertained from 

 surveys in Northern Europe, that other agents more or less subaque* 

 ous, including icebergs and great masses of drift, have produced pre- 

 cisely similar results. He cites examples in the Alps, where per- 

 fectly 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, 

 above the Baths of Pfeffers, where this ancient stiiation, undistin- 

 guishable from that caused by existing glaciers, has, by a very recent 

 slide of a heavy mass of gravel from the upper slope of the same 

 rock, been crossed by fresh scorings and striae, transverse to those 

 of former date, from which the markings made in the preceding 

 year only differ in being less deeply engraved. He also adverts to 

 the choking up of some valleys, particularly of the Vorder Rhein 

 below Dissentis, by the fracture, in situ, of mountains of limestone, 

 which constitute masses of enormous thickness, made up of innu- 

 merable small fragments, all of which have been heaped together 

 since the dispersion of the erratic blocks ; and he further indicates the 

 effects of certain great slides or subsidences within the historic sera. 



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

 opinions derived from observations in America, and says, " I feel most en- 

 tirely convinced ih&t floating ice and glaciers produce effects so similar, that 

 at present there is, in many cases, no means of distinguishing which for- 

 merly was the agent in scoring and polishing rocks. This difficulty of di- 

 stinguishing the two actions struck me much in the lower parts of the 

 Welsh valleys." 



