ICE AGES — SIMPSON 291 



about this early age, and there is no evidence that all these places 

 were glaciated at the same time, that it is useless to try to reconstruct 

 the climatic conditions which then existed. The only certain con- 

 clusion is that already stated, namely, that the temperature of the 

 earth was then already sufficiently low to allow of ice formation. 



PERMO-CARBONIFEROUS ICE AGE 



After the pre-Cambrian Ice Age, there is little or no evidence of 

 extensive ice until toward the end of the Carboniferous Period or the 

 beginning of the Permian Period, when evidence of extensive ice 

 appears. This period is called the Permo-Carboniferous Ice Age. 

 The chief regions where the ice was extensive and the evidence un- 

 doubted are in South America, South Africa, Australia, and India. 

 The latter is well within the Tropics, and the evidence is perfectly 

 clear that an extensive ice sheet existed at sea level in the Central 

 Provinces, India. It is of great importance to notice that, so far as 

 the evidence goes, the ice at this time was all situated within 40° of 

 latitude of the Equator, and mainly in the Southern Hemisphere. 

 Most geologists consider that at the same time the north polar regions 

 had much higher temperatures than at present, luxuriant vegetation 

 growing at this time in both Greenland and Spitsbergen. 



This would mean that while there was glaciation within the 

 Tropics leading to vast ice sheets at sea level, there was an almost 

 subtropical climate in polar regions. This is a reversal of the 

 climatic belts which no meteorologist can accept. Owing to the shape 

 of the earth, the equatorial belt must always be warmer than the 

 polar regions. The only explanation the meteorologist can give — 

 and it was given by Wegener — is that the continents were not then 

 in the same position relative to the Pole as they now occupy. In 

 other words, the continents have moved since Permo-Carboniferous 

 times. 



THE PLEISTOCENE ICE AGE 



After the Permian Period, there was another long stretch of time 

 without any marked evidence of ice. This interval includes the whole 

 of the Secondary and Tertiary divisions of geological time. 



Evidence of ice was not entirely absent during this period, but 

 geologists are of the opinion that the climate of the world as a whole 

 was warmer than at present. In any event there was nothing equiva- 

 lent to the extensive ice fields which left their traces in the pre-Cam- 

 brian and the Permo-Carboniferous Periods. 



The Tertiary ended with the Pliocene Period, when without doubt 

 the climate of Europe was definitely warmer than at present. Toward 

 the end of the Pliocene Period the temperature commenced to fall in 

 Europe, and evidence of ice made its appearance. Some time between 



114728—39 20 



