LIFE ON THE EARTH. 159 



buted to a considerable part at least of the hemi- 

 sphere, is twice as great in amount as in the most 

 favourable example now to be found on any part 

 of the globe. 2. The average temperature of the 

 whole area affected must be augmented by about 

 13. Though neither of these conditions may be ac- 

 cepted as very probable, we can hardly avoid be- 

 lieving the varying distribution of land and water to 

 be an important element in a just explanation of 

 ancient high climate in northern zones. 



There is indeed a further consideration which 

 deserves much attention. One characteristic of the 

 climates not very far from the equator is the small 

 range of the annual temperature, only a few degrees 

 being the full amount of vicissitude in this respect 

 through the year. Some weight must be allowed to 

 this in forming our scale of required additional tem- 

 perature; perhaps a considerable weight. Under 

 the conditions assumed in the last calculation the 

 whole of the oceanic temperatures would become 

 remarkable for very small variations from one part 

 of the year to another; and thus one characteristic 

 requisite in the life of the plants and animals of the 

 warm regions being perfectly fulfilled, it seems very 

 probable that so high an average temperature as that 

 assumed might not be required. If we allow full 

 force to this idea, and conceive the equatorial tern- 



