Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/408

Rh by forests, a portion of Britain became included within the ranges of the hyenas, tigers, rhinoceros, aurochs, and their numerous associates, some now altogether extinct, some still existing, though not found in Britain, and some yet numbered among our indigenous quadrupeds.

To this epoch may be referred such an association of extinct mammalia, with freshwater shells, all at present existing, observed by Professor Phillips in Yorkshire.

Many of these animals probably inhabited some portions of the area under review; especially the south-eastern and western parts during the epoch of the Red Crag, and at the commencement of the Glacial epoch, contemporaneously with the associations of existing and extinct or southern forms of freshwater mollusca met with in the freshwater lake deposits of Essex, and the neighbouring counties, and equivalent in part to the marine formations of the mammaliferous crag. As the climate became severer, such species may have retired, and on a favourable change of conditions have again returned to their ancient haunts, —just as we have found the testacea to have done in the neighbouring seas, under the same circumstances. Thus in England, even as Mr. Lyell has observed in the case of the mastodon in America, we have the same species of Elphas, Rhinoceros, Felis, Canis, Equus, and other genera, both before and after the drift, in the former cases accompanying species (as the Mastodon angustidens, and the Cyrena), which were never to reappear; in the latter being present during their last days, as it were, at the first birth and in-coming of creatures destined to take their places. The same probably happened with the plants. Mr. Trimmer assures me of the existence of ancient forests of oak and pine distinctly below the drift, yet equivalent to the mammaliferous crag beds. Mr. Lyell quotes the authority of Mr. Robert Brown, for the existence of the spruce (Pinus abies) in similar ancient forests on the coast of Norfolk. The latter tree no longer ranges to our islands. It has retired to the far north.

We have seen that a parallel with the conditions of the fauna of the European Seas during the Glacial epoch is now to be met with on the coasts of Boreal America—that on the eastern shores of the New World between the 40th and 60th parallels of north latitude a Boreal fauna, corresponding to that of the Scandinavian and Arctic Seas of Europe meets, without an intervening assemblage of animals comparable with that of our Celtic province, a fauna equivalent to that of the southern European Seas. The point of meeting in America marks the point of cessation of the influence of the cold currents from the Arctic Seas on the one hand and that of the warm gulf-stream on the other. It corresponds to a similar state of things in the vegetation of the neighbouring mainlands, for it indicates the northern limits of the fourth botanical