372 NATURAL SCIENCE. Nov.. 



Several American examples illustrating these views were then 

 given, and it was shown that eruptive phenomena, faults, mineral 

 veins, earthquakes, and other minor phenomena associated with 

 mountains, are well explained by them. To quote Professor Le 

 Conte : — " Leaving out the monoclinal type, which seems to belong 

 to a different category, all phenomena, major and minor, of structure 

 and of occurrences, connected with mountains, are well explained by 

 the theory of lateral pressure acting on lines of thick sediments 

 accumulated on marginal sea-bottoms and softened by invasion of 

 interior heat. This view is, therefore, satisfactory as far as it goes, 

 and brings order out of the chaos of mountain phenomena. It has 

 successfully directed geological investigation in the past, and will 

 continue to do so in the future." ^ 



This is a statement of the theory with which Professor Le 

 Conte's name has been associated, and it is one that is distinctly 

 intelligible. It, however, contains in itself a proof of the difficulty 

 of drawing a marked line between the Formal and Causal. The 

 " hydrothermal softening of the earth's crust along the line of thickest 

 sedimentation" is a physical assumption to account for certain 

 phenomena. It is also a further physical inference that ^'■lateral 

 pressure acting on lines of thick sediments, accumulated on marginal 

 sea-bottoms, and softened by the invasion of interior heat," accounts 

 for all mountain structure excepting the monoclinal type. 



I am not either affirming or denying the truth of these state- 

 ments — into which I shall examine further on, but simply wish to show 

 that the confusion of the two modes of thought complained of by Le 

 Conte in other investigators has not been altogether avoided by 

 himself; this being the case, it is only reasonable to ask if such a 

 hard and fast division be possible. 



Professor Le Conte next deals with Physical or Causal Theories, 

 which he seems to limit to an enquiry as to the cause of the lateral 

 pressure with which he builds his mountain ranges. 



First he describes what is known as the Contraction Theory, which 

 refers all lateral pressure of the crust to the interior contraction of the 

 earth: a theory which is commonly known as the "Shrunk Apple 

 Theory." It is this : The nucleus of the earth, represented by the 

 interior fruit of the apple, shrinks in bulk, while the crust remaining 

 of the same size adjusts itself to the contracting globe by folding 

 and wrinkling, like the skin of a shrunk apple. It is difficult to 

 understand, if the physical theory of the hydrothermal softening of 

 the crust can be included as part of a formal theory of mountain 

 building, why the contraction theory providing lateral pressure 

 should be put in another category. To my mind, the contraction 

 theory is as formal as the theory of mountain building we are con- 

 sidering, especially as at first understood ; for it was founded upon 



1 Nature, October 5, 1S93, pp. 551-/^ 



