Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/412

Rh my mind, that the close of the Glacial epoch was marked by the gradual submergence of some great northern land, along die coasts of which the littoral mollusks, aided by favouring currents, migrated, whilst a common flora became diffused over its hills and plains. Although I have made ice-bergs and ice-floes the chief agents in the transportation of an Arctic flora southwards, I cannot but think that so complete a transmission of that flora as we find in the Scottish mountains, was aided perhaps mainly by land to the north, now submerged. It is difficult otherwise, too, to account for the cessation of the Arctic littoral mollusks in the Scottish glacial beds, and their replacement by other forms in the English and Irish beds of the same epoch. When dredging on the great fishing-banks bounding the Zetland Isles, and forming long ridges, now in fifty and more fathoms below the sea, stretching from some unexplored point in the north, like long arms, down to the Scottish shores, and covered with angular fragments of the rocks of which they are formed, I was strongly struck with their resemblance to the rugged and broken surfaces of the neighbouring islands, and could not divest myself of the notion that these banks were submerged mountain chains. Before, however, this can be fairly assumed, we must have a re-examination of the vegetable and animal productions of Iceland, that great northern centre of volcanic power, the presence of which where it is, is possibly intimately connected with the phenomena we have been endeavouring to interpret.

The chief conclusions to which the facts and arguments stated in this essay lead, may be summed up as follows:—

1. The flora and fauna, terrestrial and marine, of the British Islands and Seas, have originated, so far as that area is concerned, since the meiocene epoch.

2. The assemblages of animals and plants composing that fauna and flora, did not appear in the area they now inhabit simultaneously, but at several distinct points in time.

3. Both the fauna and flora of the British Isles and Seas are composed partly of species, which, either permanently or for a time, appeared in that area before the Glacial epoch, partly of such as inhabited it during that epoch, and in great part of those which did not appear there until afterwards, and whose appearance on the earth was coeval with the elevation of the bed of the glacial sea, and the consequent climatal changes.

4. The greater part of the terrestrial animals and flowering plants now inhabiting the British Islands are members of specific centres beyond their area, and have migrated to it over continuous land before, during, or after the Glacial epoch.

5. The climatal conditions of the area under discussion, and north, east, and west of it, were severer during the Glacial epoch, when a great