210 SEE— TEMPERATURE, SECULAR COOLING 



I April 



at which mountains would stand, but it seems not to be attained on 

 our actual earth. We conclude therefore that even if the earth were 

 as stiff as steel and given the tetrahedral form, the corners would be 

 crushed down and the figure rapidly rounded up under its own at- 

 traction, and this deformation would also develop much internal heat. 

 As the earth, assumed to be cold, could not maintain the tetrahedral 

 form when once given it, it certainly would not tend to acquire it with 

 all except a thin crust at high temperature and kept rigid only by 

 pressure. The hypothesis of an original tetrahedral form for the 

 earth must therefore be dismissed as not even a plausible delusion. 

 § 7. The Continental and Oceanic Features of the Terrestrial Sphe- 

 roid Probably Depend on the Ruptures Produced when the Moon 

 was Formed, and the Smaller Details of the Surface are due to 

 Modifications of the Crust Made by Earthquake Forces Acting in 

 the Underlying Substratum. 



If therefore on the one hand no movements originate deep down 

 in the earth, and the effects of secular cooling at great depths have 

 little or no influence in deforming the surface, while on the other it 

 is shown that there never was a tendency for the earth's mass to 

 assume the tetrahedral form, it follows that the details of the terres- 

 trial spheroid must be explained by forces acting only in the layer just 

 beneath the crust. To suppose that any tendency to a tetrahedral 

 form can have modified the earth's surface is equivalent to the ad- 

 mission that the molecular forces are powerful, in shaping the crust, 

 in comparison with the effects of gravity. Such a view, however, is 

 known to be untenable, because under great pressure all bodies yield 

 and flow like wax, as was found in Tresca's experiments on the hard- 

 est substances, to which allusion has already been made (cf. Tresca 

 and St. Venant, " Sur Tecoulement des corps solides," Memoires des 

 Savants Btranges, Academic des Sciences de Paris, vols. 18 and 20). 

 The details of the lithosphere must therefore have been shaped by 

 forces acting beneath the crust, and such depressions of level as origi- 

 ally resulted from the detachment of the moon from the earth. That 

 the moon was originally derived from the rupture of the primitive 

 earth-mass seems to be conclusively proved by Professor Sir G. H. 

 Darwin's celebrated researches on this subject. We do not know at 

 what stage the rupture occurred, nor how much larger in volume the 



