38 PREHISTORIC EUROPE. 



be quite sure that when arctic and alpine animals were living in 

 the low grounds of France, the climate of all Europe, especially 

 the middle and northern regions, was cold and ungenial, and 

 that when hippopotamuses frequented the rivers of England, 

 very different climatic conditions prevailed. Let us try and 

 realise what those varying climatic conditions may have been. 



We have seen that the southern species are now restricted 

 to regions where, as a rule, the yearly temperature is consider- 

 ably in excess of that now experienced even in the south of 

 Europe. We have no reason to suppose, however, that such 

 a high temperature is absolutely necessary to their existence. 

 Could we but get rid of the inclement winters of the north, so 

 that no chilling frosts should affect the vegetation, it is evident 

 that the Arctic forests would gradually invade and spread over 

 the barrens and tundras. The north-temperate and temperate 

 regions would also support a more abundant growth, and wide 

 areas which are now incapable of cultivation, either by reason 

 of their elevation or their high latitude, might readily be made 

 to yield good harvests. It is quite possible, indeed, that Scot- 

 land might, under certain conditions, acquire a winter tem- 

 perature approximating to that of the south-west of France. 

 A change like this might be brought about without any revolu- 

 tion in the geographical position of our continent. Were the 

 ocean currents that even now so greatly modify our winters to 

 be very largely increased in volume, they would of course raise 

 the general temperature of the Atlantic and Northern Oceans 

 to a still higher degree, and so would effect a corresponding 

 amelioration of the climate of the neighbouring lands over 

 which the westerly winds distribute their warmth and moisture, 

 There are many good grounds for believing that considerable 

 changes in the volume of warm ocean currents have occurred 

 in the past ; and as, owing to various causes, such currents may 

 be made to flow with a greatly increased breadth and depth, so, 

 on the other hand, they may be reduced, and even turned out 

 of their course and forced to go in some other direction. But 

 no chancres in the direction or the volume of ocean currents in 



