Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/406

Rh Cancellaria costellifer is a species, found fossil in the red crag, not now known living in the European Seas, but still surviving on the coasts of North America.

These are accompanied by Nucula Cobboldiæ, and by Cardita scalaris, a crag species now extinct, and probably representative of the existing Cardita arctica. With them are a species of Astarte and a Natica, both new to me.

The examination of the Bridlington fossils has convinced me that they are truly of the age of the mammaliferous crag, and that both those formations may be referred to the epoch of the Northern Drift, and probably—especially the last mentioned—to the commencement of that epoch before the severer conditions had set in. This view is borne out by the presence of Cyrena trigonalis and Paludina unicolor (freshwater mollusks still surviving in southern regions) in freshwater beds containing mammals which do not appear after the drift along with mollusks which are common living British species now. These freshwater formations (as that of Gray's in Essex) are probably contemporaneous in part with the marine strata of the red crag. If, as I am informed by Mr. Trimmer, the Norwich crag marine beds of Bramerton alternate with freshwater beds, local phenomena of elevation and depression are indicated during the commencement of the Glacial epoch, which would account for the disappearance of some of the peculiar forms in the Norwich crag, whilst the extinction of Nucala Cobboldiæ, the Cancellaria and the Cardita, all local species, was evidently due to the conversion of the area of the crag seas into sand.

Immediately after the elevation of the bed of the great glacial sea, a great part of the area now occupied by the Celtic province of the European Seas must have been in the condition of dry land, forming extensive plains. The state of the existing fauna of the German Ocean, as compared with the fauna of that portion of our area during the Crag epochs and the commencement of the Glacial epoch, proves that the change was such as to destroy the ancient population of that sea,—doubtless through the conversion, probably gradual, of its bed into land. How far northwards this land extended it is now impossible to say, but we find the fragments of it bordering the seaside, even to the farthest parts of the mainland of Scotland. It linked Britain with Germany, Iceland, and Denmark; and a corresponding plain united Ireland with England. When considering the distribution of our flora, we derived our Germanic plants and animals from the mainland of Europe, across this ancient land. Whether the breaking up of it was slow or rapid, it