68 PREHISTORIC E UR OPE. 



I have already pointed out that severe conditions supervened 

 towards the close of the Pleistocene Period, so that a cold climate 

 followed after one that had been eminently mild and genial. 

 We are not to suppose, however, that the change was sudden. 

 It was brought about, in all probability, in the most gradual and 

 imperceptible manner throughout a long course of years. The 

 climate would become slowly deteriorated, the southern flora 

 retreating south, the arctic advancing from the north. Of the 

 mammalia, the hippopotamus, we may reasonably suppose, would 

 be amongst the first to retreat from the valleys of England, 

 France, and Germany ; but the hardier temperate forms would 

 linger on so long as they had sufficient food-supplies, and where 

 deer and oxen abounded, the carnivora would not be wanting. 

 Some of the upholders of the migration -hypothesis lay much 

 stress upon the circumstance that bones of the reindeer have 

 been found with the marks of hyaenas' teeth upon them. If 

 these marks be really due to the hyaena and not to some other 

 carnivore, the fact will only help to prove that the cave-hyaena 

 was endued with the same elasticity of constitution as the lion 

 and the tiger, and would be likely to occupy any territory 

 where there was a good supply of beef and venison. 



We must now turn our attention to the more purely geo- 

 logical evidence, when I hope to show that the conclusions we 

 have now arrived at are not only not contradicted but amply 

 supported by an impartial consideration of the physical conditions 

 under which the Pleistocene deposits were accumulated. 



