THE GLACIAL rKUlOl) 301 



slow and gradual at others, and has possibly not yet 

 entirely ceased. During the next geological period, 

 the Pliocene, the mean temperature of Europe and 

 North America became gradually lowered by the 

 setting in of new climatic conditions, which eventually 

 culminated in the Great Ice Age. 



The epoch during which this great event took 

 place is known as the Pleistocene or Glacial Period, 

 and according to one very probal)le view, we are at 

 present living in the latter part of this very period. 



The Glacial Period no doubt did not set in 

 suddenly. The foci, so to speak, of the wave of 

 long-continued cold appear to have been located at 

 the Poles, both at the beginning, during the period of 

 maximum intensity, and during the last lingering 

 phase. The cold increased in intensity slowly and 

 gradually. As the temperature fell at the North 

 Pole, a wave of cold began to creep further and 

 further southward over the greater part of Central 

 Europe and North America. When the Ice Age 

 reached its maximum, a very large portion of the 

 British Isles, Central and Southern Europe, Canada 

 and the United States, became highly glaciated — that 

 is to say, these areas resembled Greenland, as it is 

 to-day. The Alps, and all the other mountain 

 regions of the Northern hemisphere, were almost 

 entirely clothed in a mantle of snow and ice extend- 

 ing to the foothills or almost to the plains. 



In all probability the advance of the wave of low 

 temperature was exceedingly gradual, and several 



