CAUSE OF MILD POLAR CLIMATES. 157 



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 hemisphere, the geographical conditions pre- 

 venting a transference of warm water into the southern 

 hemisphere sufficient to produce 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 hemi- 

 sphere, 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 glaciated 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." * 



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 eccentricity 

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

 climates produced by the state of the northern hemi- 



* "Island Life," p. 192. 



