CHAPTER II. 



THE HYPOTHETICAL STAGES LEADING UP TO THE KNOWN ERAS. 



The hypotheses of the earth's genesis having now been sketched, 

 the several stages of evolution that led up to the beginning of the 

 legible record of Archean times claim attention. These stages are 

 as yet hypothetical, and the views presented are to be entertained 

 with appropriate reserve. The study of these stages is none the less 

 imperative, for during them the broader phases of the earth's dynamics 

 were brought into action, the essential features of its configuration 

 were determined, and even the salient lines of its relief were marked 

 out; and these have been perpetuated, in their grander features, to 

 the present time. Since these dominant characters were the outgrowth 

 of the preceding history, they are to be interpreted according as (1) 

 the forming earth is thought to have followed the gaseo-molten path, 

 with cooling as its great event, or (2) to have grown up by accessions, 

 with increasing heat and gravity as its leading features. No other 

 than these two lines of development seems to require serious con- 

 sideration at present, for, however the genetic process started, it prob- 

 ably glided into the one or the other of these alternative phases before 

 the era was reached which gave to the earth its final form. It remains, 

 therefore, to outline in succession (I) the stages of early evolution 

 under the gaseo-molten hypothesis, as commonly held heretofore; 

 (II) a modification of these stages designed to escape difficulties 

 raised by recent investigations, and (III) the stages under the 

 accretionary hypothesis. 



I. STAGES UNDER THE COMMON FORM OF THE GASEO-MOLTEN 

 (LAPLACIAN) HYPOTHESIS. 



The hypothetical stages arising from the Laplacian view have 

 nowhere been stated more definitely and succinctly than by Professor 

 Dana, 1 and his synopsis is here introduced as a typical statement of 



1 Manual of Geology, 4th edition, pp. 440,441. 



82 



