Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

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.