1872.] DAWKIN'S — CLASSIFICATION OF PLEISTOCENE STRATA. 411 



shall presently see, there is reason for the belief that it was not 

 continuous in one direction, but that there were pauses, or even 

 reversions towards the old temperate state, it follows that the two 

 groups of animals would at times overlap, and their remains be 

 intermingled with each other. The frontiers also of each of the 

 geographical provinces must necessarily have varied with the season ; 

 and the competition for the same feeding-grounds, between the 

 invading and the retreating forms, must have been long, fluctuating, 

 and severe. The passage, therefore, from the Pliocene to the 

 Pleistocene fauna must have been extremely gradual in each area ; 

 and the lines of definition between the two must be, to a great 

 extent, arbitrary, instead of being sufficiently strongly marked to 

 constitute a barrier between the Tertiary and Posttertiary groups of 

 life of Lyell, or between the Tertiary and Quaternary of the French 

 geologists. The principle of classification which I shall adopt is 

 that offered by the gradual lowering of the temperature, which has 

 left its marks in the advent of animals before unknown in Europe ; 

 and I shall divide the Pleistocene deposits into three groups : — 



1st. That in which the Pleistocene immigrants had begun to 

 disturb the Pliocene mammalia, but had not yet supplanted the 

 more southern animals. ISTo arctic mammalia had as yet arrived. 

 To this belongs the Forest-bed of ]N"orfolk and Suffolk, and the de- 

 posit at St.-Prest, near Chartres. 



2nd. That in which the characteristic Pliocene Cervidce had dis- 

 appeared. The even-toed Huminants are principalij' represented 

 by the Stag, the Irish Elk, the Roe, Bison, and Urus. Elephas 

 onendionalis and Rhinoceros etriiscus had retreated to the south. 

 To this group belong the Brick-earths of the lower valley of the 

 Thames, the river-deposit at Clacton, the Cave of Baume, in the 

 Jura, and a river-deposit in Auvergne. 



3rd. The third division is that in which the true arctic mammalia 

 were among the chief inhabitants of the region ; and to it belong 

 most of the ossiferous caves and river-deposits in Middle and North- 

 ern Europe. 



These three do not correspond with the Preglacial, Glacial, and 

 Postglacial divisions of the Pleistocene strata in Central and North 

 Britain, since there is reason to ^believe that all the animals which 

 occupied Britain after the maximum cold had passed away, had ar- 

 rived here in their southern advance before that maximum cold had 

 been reached, or, in other words, were both Pre- and Post-glacial. 



I shall first of all examine how this classification applies to Great 

 Britain. 



2. The Late Pleistocene Mammalia from British Eiver-deposits. 



The third or late division of the Pleistocene strata will be taken 

 first. The evidence that it is far older than any of the Prehistoric* 



* For definition of the term PTfcliisfcorio, see Introd. Brit. Pleistocene Mam- 

 malia, Palajont. Soc. 1866; "Prehistoric Mammalia of Great Britain," Con- 

 gress of Prehistoric Archieology, Norwich, 1868, p. 269. 



VOL. XXVIII. — PART I. 2 a 



