PART II 

 HISTORICAL GEOLOGY 



CHAPTER XII 

 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 still earlier 

 ages is indistinct, and if an attempt be made to follow the history 

 back to its 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 the 

 greatest difficulty. Still lower lies the inaccessible interior of the 

 earth whose nature is more a matter of inference than of knowledge. 



Some suggestions as to the origin of the earth may be found 

 in its relations to the other bodies of the solar system, and certain 

 features of the solar system give pointed hints as to its early history. 

 The interpretation of these outside relations and of the secrets of 

 the hidden interior is yet far from clear, and our only recourse at 

 present is to hypotheses. It is nevertheless important that we 

 should study, with due reserve, these hypotheses, and note with 

 care the ways in which they enter into the 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 OF THE EARTH'S ORIGIN 



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- 



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