ADDENDA. 617 



that of the southern hemisphere as it now is ; and consequently, as we 

 know, that the sea within recent tertiary periods stood at a higher level 

 over a large portion of our continent, it might have been affirmed, had 

 there been no record of the existence of erratic blocks on this side of the 

 globe, that it would bean anomaly, difficult of explanation, should there 

 not be found around the eminences of central and northern Europe great 

 unrolled fragments, scattered at long distances from their parent sources, 

 and often separated from them by profound valleys. 



M. Agassiz has lately {Address to the Helvetic Society, July 1837, 

 translated in Javieson's New PhilosojjhicnlJournal,vo\. xxiii., p. 364, and in 

 several communications in the French periodical L'Institut) written on the 

 subject of the glaciers and boulders of the Alps. He clearly proves, as 

 It appears to me, that the presence of the boulders on the Jura cannot be 

 explained by any debacle, or by the power of ancient glaciers driving 

 before them moraines, or by the subsequent elevation of the surface on 

 which the boulders now lie. M. Agassiz also denies that they were 

 transported by floating ice, but he does not fully state his objections to this 

 theory ; nor does he oppose it, by the argument of the apparent anomaly of 

 a low descent of glaciers, with the generally-received opinion of the more 

 tropical character of the productions of the antecedent periods, — which was 

 philosophical, until the effiscts of a temperate and equable climate were 

 considered.* On the contrary, he assumes that, during the gradual cooling 

 of the earth, there have been periods of excessive refrigeration. It is 

 needless to state that sucli an hypothesis is not supported by a single 

 fact — without, indeed, the assumed sudden renewal of life on the surface of 

 the world at successive periods be considered such. During this imagined 

 period of excessive refrigeration, the Alps and the greater part of Europe, 

 and even of Asia, are supposed to have been covered by one immense 

 sheet of ice, and during the assumed sudden elevation of the Alps, frag- 

 ments of rocks are supposed to have been shot over the frozen surface, 

 and, when the ice melted, to have dropped on the surface where they now 

 lie. M. Agassiz considers that this view explains the position of the 

 boulders on pinnacles, and their absence in the valleys. I confess I 

 should have thought, after the flexure and elevation of the ice, these 

 would have been the least probable situations : but neither this, or some 



* M. Charpentier (in his account of M. Venetz's investigations on the 

 Glaciers of the Falais — Edinburgh New Philosophical Journal, vol. xxi., p. 

 213) was fully aware of this difficulty. His explanation rests on a sup- 

 posed enormous oscillation of level in the Alps,— an assumption which is 

 unsupported by other facts, and is not applicable to the general case of 

 Europe. 



