Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/308

214 sea, and here and there occupy in the winter the pastures that afforded food to Preglacial or Pliocene mammals in the summer. And in this way the remains of animals indisputably Preglacial or Pliocene may be mingled with those indisputably Postglacial or Quaternary in the deposits of the same stream. Thus the presence of the R. megarhinus and of the hardier members of the Preglacial fauna, the Red Deer, Horse, Urus, and possibly C. megaceros, in association with the Mammoth, Tichorhine Rhinoceros, and Musk- sheep may be accounted for. On these grounds the deposits in question have been separated from the ordinary Postglacial series. They probably form the first terms of the Postglacial series, and point back to a time when the Postglacial invaders had not taken full possession of the district. And inasmuch as no North- Asiatic mammal has yet been found at Clacton, while several have been found in the Lower Brickearths, the former is considered of higher antiquity than the latter. They bridge over that vast interval between the Preglacial or Pliocene and the Postglacial or Quaternary epochs that is sharply marked in Britain north of the Thames by the deposit of the Boulder-clay, but which in the south of England and in France and Italy is not clearly defined. On this hypothesis the passage from the Pliocene to the Postglacial series would be as follows: — 1, Pliocene of France and Italy; 2, Preglacial (? Pliocene) of Forest-bed ; 3, Passage-bed of Clacton ; 4, Postglacial Passage- beds of the Thames valley ; 5, Postglacial series. I am unable to offer any opinion about the identity of the Forest-bed fauna with that of the foreign Pliocenes.

There is also another point bearing on the question of the relation of the Pliocene to the Postglacial fauna that I have referred to this place, the occurrence of the Pliocene Machairodus in the midst of the remains of Reindeer, Cave-hyaena, Mammoth, Tichorhine Rhinoceros, and other characteristic Postglacial mammals. Its presence can only be accounted for on the supposition that it strayed northwards from its southern habitat, very much after the fashion of its living congener the Tiger of Northern Asia. There is nothing more improbable in the idea that a small body of southern carnivores should have preyed upon the Reindeer in the neighbourhood of Kent's Hole than that a Tiger specifically identical with that of India should at the present day find convenient food among the herbivores of Siberia. It indicates, however, one important fact, that while the Postglacial mammals were in full occupation of Britain, the Pliocene fauna to which belongs Machairodus occupied a zoological province further to the south.

13. Postglacial Climate. — We have now, in conclusion, to consider what was the nature of the climate under which the Postglacial mammals lived. Sir Charles Lyell and the authors of the 'British Pleistocene Mammalia ' agree in the belief that it was continental in character, while Britain formed a part of the Postglacial continent, or, in other words, that the extreme cold of winter and the extreme summer- heat were more intense than in the present condition of things. The evidence of the contorted gravels, and the traces of terrestrial glacial