216 lRature'0 /HMracles. 



Alaska. This might be produced hy a change 

 in the conditions of the equatorial current, so 

 that evaporation would be more rapid in the 

 northern Pacific than it now is. When we 

 consider that evaporation increases in pro- 

 portion as the heat increases, we can see that 

 heat is just as important a factor in the pro- 

 duction of glaciers as cold. If evaporation 

 could be increased in the Pacific Ocean west 

 of Alaska, which would be carried by the wind 

 over the mountains upon the land, and pre- 

 cipitated as snow, the great glaciers in that 

 region would begin to grow instead of gradu- 

 ally receding, as is the case at present, and 

 this without any change in the temperature of 

 the world as a whole or in the amount of heat 

 received from the sun. One can readily see 

 how changes in the elevation of the bottom of 

 the ocean would have such an effect upon the 

 tropical stream as would either increase or de- 

 crease the temperature of the thermal river 

 that flows up the western coast of Alaska. 



Whatever may have been the cause that 

 created the great ice age in North America, 

 so that a sheet of ice covered considerably 

 more than half of the continent, there is no 

 doubt in regard to the fact of the existence of 

 such an age, and it will be interesting to study 

 some of the physical changes that have been 

 made by the ice at that period on the surface 

 of the glaciated area. 



