130 
ISLAND LIFE. 
[part I. 
stratum of air 800 feet thick from the freezing point to the 
tropical heat of 88° F. ! We thus obtain a good idea, both of 
the wonderful power of snow and ice in keeping down tempera- 
ture, and also of the reason why it requires so long a time 
to melt away, and is able to go on accumulating to such an 
extent as to become permanent. These properties would, how- 
ever, be of no avail if it were liquid, like water ; hence it is 
the state of solidity and almost complete immobility of ice 
that enables it to produce by its accumulation such extra- 
ordinary effects in physical geography and in climate, as we 
see in the glaciers of Switzerland and the ice-capped interior 
of Greenland. 
High Land and great Moisture essential to the initiation of a 
Glacial epoch . — Another point of great importance in connection 
with this subject, is the fact, that this permanent storing up of 
cold depends entirely on the annual amount of snow-fall in pro- 
portion to that of the sun and air-heat, and not on the actual 
cold of winter, or even on the average cold of the year. A 
place may be intensely cold in winter and may have a short 
arctic summer, yet, if so little snow falls that it is quickly melted 
by the returning sun, there is nothing to prevent the summer 
being hot and the earth producing a luxuriant vegetation. As 
an example of this we have great forests in the extreme north 
of Asia and America where the winters are colder and the 
summers shorter than in Greenland in Lat. 62° N., or than in 
Heard Island and South Georgia, both in Lat. 53° S. in the 
Southern Ocean, and almost wholly covered with perpetual snow 
and ice. At the “ Jardin ” on the Mount Blanc range, above 
the line of perpetual snow, a thermometer in an exposed situa- 
tion marked — 6° F. as the lowest winter temperature : while in 
many parts of Siberia mercury freezes several weeks in winter, 
showing a temperature below — 40° F. ; yet here the summers 
are hot, all the snow disappears, and there is a luxuriant vege- 
tation. Even in the very highest latitudes reached by our last 
Arctic Expedition there is very little perpetual snow or ice, for 
Captain Nares tells us that north of Haye’s Sound, in Lat. 79° 
N., the mountains were remarkably free from ice-cap, while 
extensive tracts of land were free from snow during summer, 
