Mild Polar Climates. 277 



rise at the pole. Supposing there had been a rise of, say, 30° 

 at the pole resulting from a fall of 10° at the equator (and this 

 is by no means an improbable assumption), this would reduce 

 the difference between the equator and the pole by 40°, or to 

 half its present amount. We should then have a climatic con- 

 dition pretty much resembling that which is known to have 

 prevailed during at least considerable portions of the Tertiary 

 period. 



It is indeed very doubtful if such a climatic condition of 

 things as that could be brought about by a high state of eccen- 

 tricity with the present distribution of land and water ; but, on 

 the other hand, it is just as doubtful whether the channels of 

 communication assumed by Mr. Wallace could have brought 

 it about without the aid of eccentricity. 



The very existence of so high a temperature on the northern 

 hemisphere during Tertiary times may be regarded as strong 

 presumptive proof that the geographical conditions obtaining 

 on the southern hemisphere were most unfavourable to the 

 flow of intertropical water into that hemisphere. This may 

 be one of the reasons why a high state of eccentricity failed 

 to produce a well-marked glacial epoch on the northern hemi- 

 sphere, the geographical conditions preventing a transference 

 of warm water into the southern hemisphere sufficient to pro- 

 duce true glaciation on the opposite hemisphere. That the 

 geographical conditions obtaining on the southern hemisphere 

 during Tertiary times were probably of such a character is an 

 opinion advanced by Mr. Wallace himself. "There are," he 

 says, " many peculiarities in the distribution of plants and of 

 some groups of animals in the southern hemisphere, which 

 render it almost certain that there has sometimes been a 

 greater extension of the antarctic lands during Tertiary times ; 

 and it is therefore not improbable that a more or less glaci- 

 ated condition may have been a long-persistent feature of 

 the southern hemisphere, due to the peculiar distribution of 

 land and sea, which favours the production of ice-fields and 

 glaciers" (p. 192). 



Influences of Eccentricity during the Tertiary Period. — This 

 being the state of things on the southern hemisphere, the 

 glacial condition of the hemisphere, when its winter solstice 

 was in aphelion, would tend in a powerful manner to impel 

 the warm water of the south over on the northern hemisphere, 

 and thus raise its temperature. This, again, is a view which 

 has also been urged by Mr. Wallace. " Though high eccen- 

 tricity would," he remarks, " not directly modify the mild 

 climates produced by the state of the northern hemisphere 

 which prevailed during Cretaceous, Eocene, and Miocene 



