166 DISCUSSIONS IN CLIMATOLOGY. 



than they would have in lowering the temperature of 

 that hemisphere when the winters were in aphelion. 

 At the periods 2,500,000 and 850,000 years ago, 

 for example, those physical agents would no doubt 

 produce quite a tropical condition of climate in high 

 northern latitudes when the winters were in peri- 

 helion, while it is quite probable they may not have 

 been able to produce glaciation when the winters were 

 in aphelion. It is more than likely that the tropical 

 nature of the climate during portions of the Tertiary 

 period was due not so much to that peculiar distribu- 

 tion of land and water existing then, as it was to the 

 fact that this peculiar distribution enabled the physical 

 agents in operation during a high state of eccentricity 

 to impel a vastly greater amount of warm intertropical 

 water into the temperate and Arctic seas than they 

 could have done under the present geographical condi- 

 tion of things. 



Those very same geographical conditions enabling 

 the physical agents to raise the temperature excep- 

 tionally high during the warm periods would, on the 

 other hand, prevent them from being able to lower 

 the temperature exceptionally low during the alter- 

 nate cold periods. Nevertheless, I think it probable 

 that at the two periods referred to, when the eccen- 

 tricity was much greater than it was during the Glacial 

 Epoch, the temperature would be lowered to an extent 

 that would produce glaciation, although the glaciation 

 might not perhaps approach in severity to anything 

 like that of the Glacial Epoch. The negative evidence 

 which has been adduced against the existence of such 

 glacial conditions during the Tertiary period is cer- 

 tainly far from being conclusive. 



The opinion is concurred in by Mr. Wallace that the 

 Table of Eccentricity for the past three million years, 



