8 PLEISTOCENE MAMMALIA. 



southwards (luring' the winter, and thus the two sets of bones became associated. 

 This theory was proposed long before modern research had shown the existence 

 of great fluctuations of climate during palaeolithic times. 



James Geikie opposed this theory on several grounds. For geographical and 

 meteorological reasons he maintained that if the winter conditions in Britain 

 were such as to produce a type of winter with cold comparable to that of Siberia, 

 summer conditions would have been colder than in Siberia and the southern 

 animals could not possibly have lived. Putting aside climatic considerations, he 

 pointed out that the hippopotamus is not, properly speaking, a migratory animal. 

 Lastly, the association of hippopotamine bones with shells like Cyrena fluminalis 

 and Unio littoralis, which are not now found nearer Britain than North Africa, is 

 inconsistent with the existence of very cold winters. 



(3) That of Climatic Change. — Tins theory assumes that general changes of 

 climate took place during the accumulation of the bone-bearing deposits. It was 

 advocated in one form or another by nearly all the earlier writers on the subject, 

 such as Lyell 1 and .). Geikie, and is strongly supported by modern research. 

 There are two modifications of it. According to J. Geikie the deposits containing 

 Hippopotamus and other southern forms were accumulated during mild inter glacial 

 periods. By the majority of students of the subject the climatic changes are believed 

 to be later than the main glaciation, the deposits with Hippopotamus being assigned 

 to the Chellean or oldest palaeolithic stage. In the Riviera the hippopotamus 

 survived to a later period, being found in Auriguacian caves near Mentone. 



A fourth possible explanation of some at any rate of the eases in which 

 southern and boreal forms are stated to be associated lies in error of observation 

 or of determination. Boule 3 has laid much stress on this point. He shows that 

 through error of observation bones which are in reality derived from an older 

 deposit may be thought to be of the age of that in which they are found, while 

 in other eases, e.g. the reported occurrence of the boreal form Rhinoceros 

 tichorhinus with Hippopotamus at Harrington near Cambridge, the supposed 

 association was due to wrong: determination, the Barrington rhinoceros being; 

 B. merchii. 



[II. DESCRIPTION OF THE SKELETON. 



The Hippopotamidse agree with the other Suina, the pigs and peccaries, in the 

 fact that the 3rd and fth metacarpals and metatarsals remain distinct. The full 

 series of 44 teeth is often present. 



1 ' Principles of Geology,' 10th ed., i, chap. 10. * ' Geol. Mag.,' ix (1872), p. 164. 

 3 'Bull. Soc. Geol. France." [4], vii (1907), p. 382, and ' Les Grottes de Grimakli,' i, fasc. o 

 (1910), p. 194. 



