12. The relationship now existing between the faunas and floras of Boreal America and Europe, both marine and freshwater, was established during (probably towards the close of) the Glacial epoch.
13. No glacial beds are known in southern Europe; no "newer pliocene" (in the sense of equivalents of the Sicilian tertiaries), in the centre and north. In the latter we find most of the existing British testacea, which after inhabiting our area before, disappeared from it during the Glacial epoch; and with them we find certain glacial species of northern origin, now extinct in the seas of southern Europe. I infer the synchronism of the glacial and Sicilian deposits.
Throughout this essay I have used the epithet "glacial," in connexion with the words "epoch," "beds," and "formation," in a sense which purists in geological phraseology may consider objectionable. I have used it, however, for want of a better, and as an expression of convenience, always intending to express by the phrase "Glacial epoch" that section of geological time which was typically distinguished by the
A writer, evidently well versed in the subject, in the 'Phytologist,' for March, 1846, sums up our present knowledge of the Azorean flora as follows:—"The number of species absolutely limited to the Azores is rather less than stated by Seubert, while the number of species common to them and to Madeira requires to be taken at a higher figure. Speaking in round numbers, we may say that four-fifths of all the species now wild in the Azores are wild also in Europe, from which many of them have been doubtless carried to the Azores by the early settlers. Of the remaining one-fifth, nearly the whole number are peculiar to the Azores, or to the Archipelago of the Atlantic Islands, which includes also Madeira and the Canaries. Some have emigrated to the Azores from the continents of Africa and America." The floras of Madeira and the Canaries indicate their proximity to the ancient bounds of the great Mediterranean flora, to the ancient subtropical African province, of which the Cape de Verde Isles probably present us with fragments. (For the flora of the Canaries see the great work of Webb and Berthollet.)
In the Gallapagos Islands we have a group which come under Strabo's second class; and, since they lie not farther from the South American mainland than the Azores do from Europe, and moreover have the advantage of lying in the course of a great current (Humboldt's or the Peruvian current) flowing towards them from the American shores, and therefore likely to be a powerful agent in the diffusion of organic forms, they afford us a good opportunity of comparing the features of organic life in islands of the first class with those in such as are distinctly of the second. The researches of Mr. Darwin and of Dr. Joseph Hooker, have furnished good data for such comparison. What is the result? That in these islands, which were never united with the mainland, we have distinct systems of creatures related to those of the nearest land, by representation or affinity, and not by identity. "The natural history of those islands," writes Mr. Darwin, in his admirable 'Journal of Researches,' "is eminently curious, and well deserves attention. Most of the organic productions are aboriginal creations found nowhere else; there is even a difference between the inhabitants of the different islands; yet all show a marked relationship with those of America, though separated from that continent by an open space of ocean between 500 and 600 miles in width. The Archipelago is a little world itself; or, rather, a satellite attached to America, whence it has derived a few stray colonists, and has received the general character of its indigenous productions; considering the small size of these islands, we feel the more astonished at the number of their aboriginal beings, and at their confined range."—(Second Edition, p. 376.)
