Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/364

view I have put forward respecting the origin of the flora of the British mountains be true—and every geological and botanical probability, so far as that area is concerned, favours it—then must we endeavour to find some more plausible cause than any yet shown, for the presence of numerous species of plants, and of some animals, on the higher parts of alpine ranges in Europe and Asia, specifically identical with animals and plants indigenous in regions very far north, and not found in the intermediate lowlands. Tournefort first remarked, and Humboldt, the great organizer of the science of natural-history geography, demonstrated, that zones of elevation on mountains correspond to parallels of latitude, the higher with the more northern or southern, as the case might be. It is well known, that this correspondence is recognised in the general facies of the flora and fauna, dependent on generic correspondences, specific representations, and, in some cases, specific identities. But when announcing and illustrating the law that climatal zones of animal and vegetable life are mutually repeated or represented by elevation and latitude, naturalists have not hitherto sufficiently (if at all) distinguished between the evidence of that law, as exhibited by representative species and by identical. In reality, the former essentially depend on the law, the latter being an accident not necessarily dependent upon it, and which has hitherto not been accounted for. In the case of the alpine flora of Britain, the evidence of the activity of the law and the influence of the accident are inseparable, the law being maintained by a transported flora, for the transmission of which, I have shown, we can account by an appeal to unquestionable geological events. In the case of the Alps and Carpathians, and some other mountain ranges, we find the law maintained partly by a representative flora, special in its region, i. e., by specific centres of their own, and partly by an assemblage more or less limited in the several ranges of identical species, these latter in several cases so numerous that ordinary modes of transportation now in action can no more account for their presence than they can for the presence of a Norwegian flora on the British mountains. Now, I am prepared to maintain, that the same means which introduced a subarctic (now mountain) flora into Britain, acting at the same epoch, originated the identity, so far as it goes, of the alpine floras of middle Europe and central Asia. For now that we know the vast area swept by the glacial sea, including almost the whole of central and northern Europe, and belted by land, since greatly uplifted, which then presented to the water's edge those climatal conditions for which a subarctic flora—destined to become Alpine—was specially organized, the difficulty of deriving such a flora from its parent north, and of diffusing it over the snowy hills bounding this glacial ocean, vanishes, and the presence of identical species at such distant points remains no longer a mystery. More-