CHAP. IX 



MILD ARCTIC CLIMATES 



199 



accumulating and storing up heat or cold from one year to 

 another, though they do in a pre-eminent degree possess 

 the power of equalising the temperature of winter and 

 summer and of conveying the superabundant heat of the 

 tropics to ameliorate the rigour of the Arctic winters. 

 However great was the difference between the amount of 

 heat received from the sun in winter and summer in the 

 Arctic zone during a period of high excentricity and 

 winter in aphelion, the inequality would be greatly dim- 

 inished by the free ingress of warm currents to the polar 

 area; and if this was sufficient to prevent any accumu- 

 lation of ice, the summers would be warmed to the full 

 extent of the powers of the sun during the long polar day, 

 which is such as to give the pole at midsummer actually 

 more heat during the twenty-four hours than the equator 

 receives during its day of twelve hours. The only 

 difference, then, that would be directly produced by the 

 changes of excentricity and precession would be, that the 

 summers would be at one period almost tropical, at the 

 other of a more mild and uniform temperate character; 

 while the winters would be at one time somewhat longer 

 and colder, but never, probably, more severe than they are 

 now in the west of Scotland. 



But though high excentricity would not directly modify 

 the mild climates produced by the state of the northern 

 hemisphere which prevailed during Cretaceous, Eocene, 

 and Miocene times, it might indirectly affect it by in- 

 creasing the mass of Antarctic ice, and thus increasing the 

 force of the trade-winds and the resulting northward- 

 flowing warm currents. Now there are many peculiarities 

 in the distribution of plants and of some groups of animals 

 in the southern hemisphere, which render it almost certain 

 that there has sometimes been a greater extension of the 

 Antarctic lands during Tertiary times ; and it is therefore 

 not improbable that a more or less glaciated condition may 

 have been a long persistent feature of the southern hemi- 

 sphere, due to the peculiar distribution of land and sea 

 which favours the production of ice-fields and glaciers. 

 And as we have seen that during the last three million years 

 the excentricity has been almost always much higher than 



