Where did Life Begin? 55 



the temperature of the tropics and the polar 

 zones in the past than we find existing between 

 them to-day. For even such a condition and 

 difference of temperature would have given 

 to the polar regions first a tropical climate 

 and life, then a temperate climate and life 

 appropriate to it, and each for an immense 

 epoch before the equatorial belt would have 

 been habitable for any known organism. 



VII. 



One glance at the immediate cause — the 

 proximate moving power — of all this vast, va- 

 ried, and complex machinery and movement 

 of life, and I have done. We have been thus 

 far contemplating and discussing the results 

 of this power ; attempting a partial description 

 of the methods made manifest in Its grand life- 

 bearing and eliminating work ; discovering its 

 ways in prompting, developing, sifting, and 

 destroying life ; following in the paths and ex- 

 amining the effects of its great zones or belts 

 of graded climates girding the earth, and which 



