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

612 ADDENDA. shells not existing there. We may also suppose that he had discovered that the limits of the more tropical forms, both animal and vegetable, of the productions of the land, had likewise during this former period extended further south: vifhat, then, would he say? Would he not at once infer, witli the strongest appearance of truth, that the climate formerly had a more tropical character, properly so called, and therefore had a higher annual mean temperature tlian at present? Nevertheless, we know such an inference would have been absolutely erroneous. To put the case in another point of view : should a geologist find, in lat. .39°, on the coast of Spain, a tertiary deposit, abounding with Olivas, Volutas, and Terebras ; or in lat. 43^, on the coast of France, other beds, containing a large Voluta, and n\imerous Patellae, Fissurellte, Chitons, and Balani, larger and of stronger growth than the existing species, would he be justified, after what is now known, in pronouncing thiit the climate formerly had a higlier mean temperature ? I think it may be safely asserted that he would not be so justified, but rather would be bound to search for other evidence. In the actual case of Europe, we have knowledge (as will be shown in a following note*) of another element in the problem, namely of the lower descent during former times of the snow-line, — as is inferred from the former low descent of glaciers, on the same moun- tains, where they now occur only at great heights, and likewise from the congelation during this same period of the soil in a low latitude — and this new element, I believe, gives the key to the solution of the problem, which is, that the climate of Europe was formerly more equable, but so far from being strictly more tropical, that it probably even had a lower mean annual temperature than it now possesses. I need scarcely say that I here refer only to the later tertiary periods : in the more ancient epochs, the plainest analogies tell us of an equatorial climate, whilst on the other hand, we are very far from having the smallest reason to sup- pose that the snow-line then descended low ; and this is the key, as Ihave called it, to the problem of later times. Page 282. With respect to ice transporting fragments of rock in the Antarctic regions, M. Cordier, in his instructions fUInstitut, 1837, p. 28.S^ to the voyage of the Astrolabe and the Zelee, has this passage : " Les relations de I'expedition anglo-americaine de decouverte execut^e en 1830, nous ont * As these notes are appended to the Journal, I have found it scarcely possible to classify them properly. I have been obliged to allude to the lower descent of the glaciers in Europe during former periods — facts which are first brought forward in a succeeding note to p. 294.