ch. viu.] THE BEGINNINGS OF LIFE. 435 



aggregations of matter. By following out this method new 

 light will no doubt eventually be thrown upon the past his- 

 tory of our planet, and a sound basis will be obtained for 

 conjectures regarding the existence of living organisms upon 

 some of our neighbour worlds. 



In this account of the matter we have completed, so far as 

 is needful for the purposes of this work, our exposition of 

 the evolution of the earth. Combining the results obtained 

 in the three foregoing chapters, we may contemplate in a 

 single view the wonderful advance in determinate multi- 

 formity which has resulted from the integration of the earth's 

 matter, with the accompanying dissipation of its internal 

 motion. We have witnessed this process of evolution as 

 manifested in geologic and meteorologic phenomena ; we have 

 followed the wondrous differentiations and integrations of the 

 molecular motion which the cooling and consolidating earth 

 has received from the centre of our system ; and finally, from 

 that very cooling and consolidation upon which all the fore- 

 going phenomena are dependent, we have shown that there 

 must naturally have ensued a progressive chemical hetero- 

 geneity, resulting at last in the genesis of compounds mani- 

 festing those properties which we distinguish as vital. Thus 

 the continuity in cosmic evolution is grandly exhibited, and 

 we see more clearly than ever that between the various pro- 

 vinces of natural phenomena there are no sharp demarca- 

 tions. As the geologic development of the earth is but a 

 specialized portion of the whole development of the solar 

 system, — a portion which we separate from the rest and 

 assign to a special science, solely for convenience of study ; 

 so the development of living matter is but a specialized por- 

 tion of the whole development of the earth, and it is only 

 for reasons of convenience that the formation of primeval 

 protoplasm is assigned to a different science from that wMdh 

 deals with the formation of limestone or silica. Though as 

 we advance from a lower grade of heterogeneity to a higher 



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