616 



ADDENDA. 



frigid zone, are the results of a climate which appears favourable to th6 

 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 the 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. 



