192 
ISLAND LIFE. 
[part t. 
important alteration of tlie climates of the temperate and Arctic 
zones so long as favourable geographical conditions, such as 
have been now sketched out, render the accumulation of ice 
impossible. The effect of a high excentricity in producing a 
glacial epoch was shown to be due to the capacity of snow and 
ice for storing up cold, and its singular power (when in large 
masses) of preserving itself unmelted under a hot sun by itself 
causing the interposition of a protective covering of cloud and 
vapour. But mobile currents of warm water have no such 
power of 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 diminished by the free ingress of warm currents to 
the polar area; and if this was sufficient to prevent any 
accumulation 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 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 pre- 
cession 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 increasing the mass of Antarctic 
ice, and thus increasing the force of the trade-winds and the re- 
sulting 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 
