THE EVOLUTION OF THE EARTH 



pendence upon the condition of all the other 

 parts. 1 



It is now sufficiently proved that the devel- 

 opment of the earth, like the development of 

 the planetary system to which it belongs, has 

 been primarily an integration of matter and 

 dissipation of motion, and secondarily a change 

 from indefinite homogeneity with relative isola- 

 tion of parts to definite heterogeneity with rel- 

 ative interdependence among parts. But our 

 survey of telluric evolution is as yet far from 

 complete. While enough has been said con- 

 cerning the redistributions of matter which have 

 gone on over the face of the globe, nothing 

 has been said concerning the far more wonderful 

 and interesting redistributions of the molecular 

 motion which the earth is continually receiving 

 from the sun. Here, as already briefly hinted, 

 we have the chief source of terrestrial heteroge- 

 neity. In the chapter on the Law of Evolution 

 it was observed, as a general truth, that homo- 

 geneous forces incident upon a heterogeneous 

 aggregate undergo differentiation and integra- 

 tion. We shall now find this general truth beau- 

 tifully exemplified in the history of the surface 



1 [These meteorological conclusions, current at the time 

 when Fiske wrote, would probably have been a good deal 

 modified had he rewritten this chapter in the light of present 

 opinion. ] 



3*3 



