Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/418

Rh At the southern bound of the dark-blue region a molluscanfauna, equivalent to the Lusitanian on the European side of the Atlantic, meets with one of a Boreal character. A similar feature is presented by the drift fossils of the pale-blue region at the point of meeting with the yellow, on the European side.

It is to be observed, that within the blue region all pleistocene fossiliferous beds contain fossils of the glacial type; and that south of it within the yellow the fossils of the equivalent beds are of the Sicilian newer pleiocene type.

The purple lines and bounds mark spots and provinces wherein we now find a flora, or the fragments of a flora, of an Arctic or truly Boreal character. It will be observed that in Europe this flora is indicated as fragmentary, and marks the lines of mountain chains, whilst in the new world (within the dark-blue line) it indicates constant Boreal regions of vegetation.

The yellow marks a region, the greater part of which was probably continuous land between the close of the meiocene epoch and the commencement of the pleistocene. The Gulf-weed bank, repeating the form of the meiocene coasts of the Old World, indicates its Atlantic bounds. Over this region I suppose the Asturian flora to have migrated to Ireland, and afterwards (during the Glacial epoch) to have been isolated, and in great part destroyed. This was a region of shallow sea during the Meiocene epoch, bounded by a gulf of deep water, dividing the marine zoological provinces of the old world from those of the new.

The lines of colour mark the regions of existing floras.

1st. The purple, already mentioned, marks the region of Arctic and Boreal floras.

2nd. The orange encircles the region of the Mediterranean flora, and includes the fragments of the ancient post-meiocene land. During such a condition of things as prevailed during the Glacial epoch (judging from the present state of the opposite side of the Atlantic), the orange line then extended farther north, and approached the purple, then circumscribing most of the land within the blue region.

3rd. The green bounds the region of the existing Germanic flora, and includes the space elevated at the close of the Glacial epoch, when the orange and purple lines receded from each other. The extension of this land included Iceland, where we now find a considerable assemblage of Germanic plants isolated.