130 



ISLAND LIFE. 



[PABT 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, 



