40 



TITB BONE-CAVR OR FISSURR OV T)IIKT)TTAM POWN. 



(,ow.ar(1a the equator. In the smnmer time the Ronfhorn 

 species would pass northwards, and in the winter time the 

 northern animals would swing southwards, and thus occupy 

 at different times of the year the same tract of ground as is 

 now the case with the elks and reindeer. It must not, how- 

 ever, bo supposed that the southern animals migrated from 

 the Mediterranean as far north as Yorkshire, or the northern 

 as far south as the Mediterranean, in one and the same yea-r. 

 There were secnlar changes of climate in Pleistocene EurO]io, 

 and while the cold was at its maximum the Arctic animals 

 arrived at the southern limit, and while it wiis at, its mini- 

 mum the spotted hya3na, hippopotamus, and other southern 

 animals roamed to the north limit. Thus every part of the 

 middle zone has been successively the frontier between the 

 northern and southern groups of animals, and consequently 

 their remains are mingled together in the caverns and river 

 deposits under conditions which prove them to have been 

 practically contemporaneous in the same region. In this 

 way the association of northern and southern animals may 

 bo explained, namely, by their migrations according to the 

 seasons, and their association over so wide an aren, as the; 

 middle zone, by the secular changes of climate, by which 

 each part of that zone in turn was traversed by the advanc- 

 ing and retreating animals. 



The identity of the British Pleistocene fauna with that of 

 the Continent leads irresistibly to the conclusion that in the 

 Pleistocene age Britain was connected with the adjacent 

 countries by " a bridge of land," over whloli tlio wild iuiimaJs 

 had free means of migration. Soundings show that Britiiin 

 and Ireland constitute merely the uplands of a plateau now 

 submerged to the extent oE al)out 100 fathoms on the mar'gin 

 of the Atlantic. An elevation to this extent would convoi-t 

 Ireland, England, and the surrounding sea,s into a pjirt of 



