160 LIFE ON THE EAKTH. 



perature to be lowered (as it would be) by an effec- 

 tive distribution of part of its warmth by currents 

 directed toward the poles, the difficulty would be 

 much reduced. 



For those who are not satisfied with the proba- 

 bility of the explanation just examined, another hy- 

 pothesis is ready, the displacement of the axis of 

 the earth. Though this is refused by the proper 

 authorities, the astronomers, it may be worth while 

 to mention that the centre of gravity of the earth 

 cannot be regarded as having been always absolutely 

 fixed when we remember the irregular distribution 

 of the axes of elevation of different periods, the 

 very considerable mass of the elevated mountain- 

 chains, and the great amount of subsidence by which 

 the areas of deposition have been affected at different 

 times. But if the centre of gravity of the earth be 

 allowed to be thus inconstant in position, the axis 

 of rotation must be subject to change from the same 

 cause. Such minute variations, however, would be 

 of small efficacy in regard to the matter in hand, if 

 we are to judge by the actual distribution of the 

 masses of elevated land, and the direction of the 

 depths of the sea. Even if we could place an extra 

 load on one meridian between the pole and the 

 equator, and thus cause an angular deviation of the 

 axis, this is a process requiring long perseverance 



