1846.] MURCHISON ON THE SCANDINAVIAN DRIFT. 351 



ceeding from the north, which, conveying coarse materials along 

 with it, had worn away and ground down all natural asperities form- 

 ing the " Stoss Seite " or weather side of the rock, such materials 

 (the impetus of their transport being checked) having been deposited 

 under tlie lee or " south " side of the elevation. But neither in these, 

 nor in other collateral observations, was it supposed that the opera- 

 tion had taken place when the rocks of Sweden so affected were 

 beneath the sea, nor was any clear distinction drawn between the 

 greatly water-worn rounded materials (which with sands form the 

 mass of the Osar) and the angular erratic blocks on the surface. 

 It was only when the subject of terrestrial glacial action w as brought 

 prominently before the scientific public by the researches of Venetz, 

 Charpentier and Agassiz in the Western Alps, that geologists and 

 naturalists began clearly to see, that although water may have been 

 the agent by which great masses of drift and sand have been spread 

 over the low countries of Europe, there might be many mountain 

 localities where glaciers formerly existed, to the advance of which, 

 as well as to their melting and dispersion, many of the superficial 

 phaenomena in question, particularly the ^^blocs perches" might be 

 due. 



Dwelling upon the great truths which his contemporaries and 

 himself had worked out in the Alps, Professor Agassiz pursued his 

 favourite hypothesis with an ardour which has always seemed to me 

 unsupported by reason, and endeavoured to show that true terres- 

 trial glacial action once extended over nearly the whole of northern 

 Europe, covering all those tracts, whether in the British Isles or on 

 the Continent, where the surfaces of rocks are worn down, polished 

 and striated in a manner resembling that observed in the Alps. 

 This bold but hasty generalization was however soon restricted to 

 what is apparently its legitimate range by the publication of Pro- 

 fessor James Forbes's work on the Alps, in which it is clearly de- 

 monstrated, from actual experiments on the motion of the glaciers 

 themselves, that such bodies never do and never can advance ex- 

 cept in tracts where they are backed by lofty mountains, so that 

 the accumulated and condensed snow may be pressed forward by 

 constantly increasing masses, and moved by its own gravitation on 

 an inclined surface*. 



Without here entering farther into the question of what tracts 

 now exempt from them may formerly have been subjected to the 

 advance of true terrestrial glaciers, and not now discussing the case 

 of Snowdon and other elevated points of Britain to which Dr. Buck- 

 land has called attention, since each case must be rigorously deter- 

 mined on its own merits, I now call the attention of my brother 

 geologists to the superficial phaenomena of those parts of Scandina- 

 via, in which, at all events, it will, I trust, be made quite manifest 

 that no land glaciers have ever acted. 



In all the central and southern portions of that district, and over 



* Tlie same author has shown liow ancient glaciers must have produced the 

 superficial appearances in the lofty Cuchnllin hills of Skye. 



2 A 2 



