PART II 

 HISTORICAL GEOLOGY 



CHAPTER XI 

 THE ORIGIN OF THE EARTH 



The bedded rocks of the earth's shell reveal its history far back 

 into the past with great fidelity; but the record of the earlier ages 

 is indistinct, and if we attempt to go back to the earth's beginning, 

 the indistinctness merges into obscurity. The rocks below the well- 

 bedded strata are so broken and altered, and so cut up by intrusions, 

 that their history is read with great difficulty. Still lower lies the 

 inaccessible interior of the earth whose nature is more a matter of 

 inference than knowledge. 



Some suggestions as to the origin of the earth are found in its 

 relations to the other bodies of the solar system, and certain features 

 of this system give pointed hints concerning its early history. The 

 interpretation of these outside relations of the earth and of the secrets 

 of its hidden interior is yet far from clear, and our only recourse is to 

 hypotheses; but it is important that we study these hypotheses, and 

 note the ways in which they enter into interpretations of the earth's 

 phenomena, for not a few of the leading doctrines of geology hang 

 on some hypothesis of the earth's beginning, and have no greater 

 strength than the hypothesis on which they depend. 



HYPOTHESES 



It is the nearly unanimous conviction of astronomers that the 

 solar system was evolved in some way from a nebula of some form. 

 Until recently, astronomers so generally accepted the view of La- 

 place that it came to be known as ''The Nebular Hypothesis"; 

 but the advance of knowledge makes it necessary to consider other 

 hypotheses which postulate that the solar system arose from a 

 nebula whose constitution and mode of evolution differed from that 



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