TEETIAEY PERIOD BY MEAXS OF THE MAMMALIA. 397 



than two thirds of the species being new. The proportion, how- 

 ever, of the Pliocene survivals to them being eight as compared 

 with twenty-two, shows that it is not sufficiently great to allow of a 

 classification in which the Tertiary ends with the Pliocene. It is 

 simply a new and more advanced phase of the Tertiary, similar in 

 kind to those which went before and follow after. If we turn our 

 attention to the Invertebrates, there is no break at all to be 

 observed between the Pliocene and Pleistocene, all the Pleistocene 

 forms being found in Pliocene strata, and the same continuity 

 being presented as that which we shall note presently in the 

 Vertebrates of the Pleistocene, Prehistoric, and Historic periods. 

 It is therefore obvious that the Tertiary life-period cannot in any 

 sense be viewed as having come to an end at the close of the 

 Pliocene age. 



20. TTi& Mid-Pleistocene Mammalia of Britain. 



The fluviatile deposits of Ilford and Grays Thurrock in Essex, at 

 Erith and Crayford in Kent, and at Clacton on the Essex coast, 

 present us with a group of animals intermediate between those of 

 the Early and Late Pleistocene. Their most important characters 

 are noted in the following list (p. 398), in which it will be seen 

 that JRJiinoceros megarhinus and the Hippopotamus are the only two 

 Pliocene species in the fauna ; the latter appears here for the 

 last time. It must also be remarked that Ovihos moscJiatus, dis- 

 covered by myself in 1857, and more recently by Mr. Cheadle, and 

 the Marmot, discovered recently by Mr. Elaxman Spurrell at Cray- 

 ford, show that the winter cold was severe, and that the arctic 

 Mammalia in their journey southwards had arrived as far as the 

 lower valley of the Thames. 



The climate at this time was colder than it ever had been before 

 in Britain, and was gradually passing into the glacial condition. It 

 is very likely, as I have pointed out in my paper on the Lower 

 Brick-earths of the Thames valley*, that the upper strata covering 

 the fluviatile deposits with the fossil remains are glacial, and that 

 therefore the deposits beneath are referable to the Preglacial age. 



Man is proved to have lived in the valley of the Thames at this 

 time by a flint flake, discovered by the Pv-ev. Osmond Eisher, in my 

 presence, at Crayford in 1872 t, and by a second, found at Erith by 

 Messrs. Cheadle and Woodward in 1876 J, and, lastly, by a recent 

 discovery of the relics of a palaeolithic factory at Crayford (shortly to 

 be described by Mr. Elaxman Spurrell). 



With the exception of the marmot and the musk-sheep, the 

 whole of the living species consist of animals now found only in 

 temperate or warm climates. Horses, uri, bisons, and mammoths 

 were the most abundant animals. 



* Quart. Joum. Geol. Soc. vol. xxiii. p. 91. t Geol. Mag. 1872, p. 268 



. J Proc. W. Lond. Scient. Assoc, Sept. 1876. 



