462 THE ICE AGE IK NORTH AMERICA. 



that there is a large snow-fall. For example, on the steppes 

 of Asia, and over the Rocky Mountain plateau of our Western 

 States and Territories, the average temperature is low enough 

 to permit the formation of extensive glaciers, but the snow- 

 fall is so light that even the short summers in high latitudes 

 cause it all to disappear ; whereas, on the southwestern coast 

 of South America, and in southeastern Alaska, where the 

 temperature is moderate, but the snow-fall is large, great 

 glaciers push down to the sea even in low latitudes. 



The circumstances, then, pre-eminently favoring the pro- 

 duction of glaciers, are abundance of moisture in the atmos- 

 phere, and climatic conditions favorable to the precipitation 

 of this moisture as snow rather than as rain. Heavy rains 

 produce floods, which . speedily transport the water to the 

 ocean-level ; but heavy snows lock up, as it were, the capital 

 upon dry land, where, like all other capital, it becomes con- 

 servative, and resists with great tenacity both the action of 

 gravity and of heat. Under the action of gravity glaciers 

 move, indeed, but they move very slowly. Under the influ- 

 ence of heat ice melts, but in melting it consumes an enor- 

 mous amount of force. 



In order to melt one cubic foot of ice, as much heat is re- 

 quired as would heat a cubic foot of water from the freezing- 

 point to 176° Fahr., or two cubic feet to 88° Fahr. To melt a 

 layer of ice a foot thick will therefore use up as much heat as 

 would raise a layer of water two feet thick to the temperature 

 of 88° Fahr. ; and the effect becomes still more easily under- 

 stood if we estimate it as applied to air, for to melt a layer of 

 ice only one and a half inch thick would require as much heat 

 as would raise a stratum of air eight hundred feet thick from 

 the freezing-point to the tropical heat of 88° Fahr. We thus 

 obtain a good idea, both of the wonderful power of snow and 

 ice in keeping down temperature, and also the reason why it 

 takes so long a time to melt away, and is able to go on accu- 

 mulating to such an extent as to become permanent. These 

 properties would, however, be of no avail if it were liquid, 

 like water ; hence it is the state of solidity and almost complete 



