Ch. XIII.] 



TIIi: EXCENTRICITIES OF THE ORBIT 



297 



have been run through before the excentricity reached -0747, if 

 we include all excentricities equalling -05 as periods of great 



cold. 



middle 



of the period would belong to an excentricity approaching to 



accumulation 



may 



Ca, may 



been considerably reduced, after which it 



would again begin to increase. The antecedent epoch D 

 mio*ht belong to those ages when changes in physical geo- 



graphy may 



Newer 



Independently of all astronomical considerations, it must, 



> comm 

 most ii 



tense, and the oscillations to which it was subject (p. 195), as 

 well as the retreat of the glaciers and the 'great thaw ' or 

 disappearance of snow from many mountain 



where 



the snow was once perpetual, required not tens but hundreds 

 of thousands of years. 



time would not suffice 



changes in physical geography and organic life of which we 

 have evidence. To a geologist, therefore, it would not appear 

 startling, that the greatest cold should be supposed to have 



some 



marine 



those of Brid- 



mi 



as far as the period D. 



Provided a predominance of land in high latitudes be 

 granted, the fact which would seem to me most favourable to 

 the connection of a large excentricity with an excess of cold 

 is the following : — 



By referrin 



map of Isothermal 



mean 



23°, 32°, 41° and 50 



them in their range 



from Europe to North America deflected from 13° to 18° of 

 latitude in a southerly direction in their passage from east 

 to west. The late Edward Forbes has also shown in one of 



maps 



* Memoirs of the Survey of Great Britain, vol. i. plate vn 





