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

616 ADDENDA. frigid zone, are the results of a climate which appears favourable to the passage of tropical forms beyond their proper limits, and to a vigorous native vegetation. The climate is one of an equable nature ; and this must, to a considerable degree, be the effect of the great area of ocean compared with the land of the southern hemisphere. In the northern he- misphere we have proofs, that the productions both of the land and water, during the period antecedent to the present, had a more tropical charac- ter than they now have, and there is, also, a high degree of probability that the proportional area of water was much greater. If then we judge from the analogy of the southern hemisphere, the first and simple inference from these facts, is, that the temperature of Europe was formerly more equable, though perhaps with a lower mean, than it now is. It may be asked, as a test of this inference, did the snow-line formerly descend lower than it now does ? Was the soil formerly frozen a little beneath the surface in a low latitude ? The congealed carcasses of the great Pachydermata of Siberia answer the second question ; and in my journal, I have indirectly considered the first one as answered, by the fact of the many erratic boulders of Europe having travelled from moun- tains, situated in regions where great bodies of ice do not at present descend to the level of the sea. For on the theory that these boulders were trans- ported by icebergs from glaciers, which formerly descended into the sea in latitudes where perpetual snow is not now found, or if so, only at great heights, the problem receives so simple a solution, that I did not hesitate, having the other data, to assume, that the snow-line in Europe formerly did descend much lower than it does at present. But, had I studied my subject more attentively, I might have taken a higher ground : in a note, indeed (p. 294), I have stated that according to Professor Esmark, it is certain, that the glaciers of Norway formerly descended to a lower level and I now found that some time since, Messrs. Venetz and Charpentier, and more lately M. Agassiz, have incontestably shown, from the presence of glacier-dikes or moraines, and from the polished and scratched surface of the rocks, that in the Alps enormous bodies of ice formerly descended to the borders even of the lake of Geneva, and therefore much lower than the line of present lowest descent.* With these several facts it might have been boldly asserted, that the climate of Europe formerly was like * No doubt if much more snow fell formerly than at present, the glaciers would formerly have descended somewhat lower; but as Europe now has a moderately humid climate, it is improbable in tlie highest degree (if indeed possible) that a difference of that kind could have caused the former extremely low descent of the ancient glaciers of the Alps : therefore we are compelled to attribute the difference to a change of temperature of some kind.