W. B. Taylor — Crumpling of the Earth? s Crust. 265 



It cannot be denied that the difficulty here set forth is a very 

 puzzling one. Especially inexplicable appears the instance 

 last referred to — of an unbroken range of mountain foldings 

 extending over more than a third of the globe's circumference. 

 While the force at the command of the rotating planet is 

 abundantly sufficient to accomplish the result evidently some 

 supplementary considerations are requsite to give the observed 

 direction to this force. Beyond all question, the surface of the 

 earth has been subjected to a compressing stress of tremendous 

 energy. To account for the stress is one problem ; to account 

 for its resultants is another and probably much more compli- 

 cated one. 



The mere mechanical difficulty, however, of transmitting 

 stresses through comparatively undisturbed areas of hundreds 

 of miles of a flexible, friable, and practically plastic crust — 

 with a large coefficient of viscous friction beneath — is not so 

 formidable as might at first sight appear. It must be borne in 

 mind that the pressures derived from an action so slow as from 

 century to century to be scarcely sensible, are of an order of 

 very great intensity, but of very small quantity. Under the 

 continued urgency of rapidly revolving tidal waves (though 

 also of a very minute order), there does not seem any improb- 

 ability in the supposition that with the long time element such 

 stresses may gradually be equalized or transmitted by what 

 might be termed a process of "conduction " almost indefinitely. 



From various considerations we may infer that in all geolog- 

 ical ages the progress of elevation has been in excess of that 

 of degradation by erosion ; that in all ages mountain building 

 has been at a maximum; that is, the uplifted heights have been 

 the greatest which the average thickness of the crust at the 

 time was capable of supporting ; so that the former has been 

 a constant function of the latter, the ratio being probably not 

 far from one-fifth. 



We may also infer that this increasing maximum of eleva- 

 tion must now have practically reached its limit, since both the 

 processes of equatorial contraction and of internal temperature 

 reduction are going on with extreme and lengthening slowness ; 

 and the whole remaining subsidence of the inter-tropical oblate- 

 ness cannot exceed five miles, during the vast ages in which 

 the earth's rotation shall be entirely arrested. 



Looking back through the long vista of the unmeasured 

 past we behold in imagination our planet in its early youth, 

 with its expanded tropical surface as yet unmarked by 

 wrinkles, endowed with superfluity of rotary activity, and sub- 

 ject to far more energetic tides and winds and tempests than 

 we know at present. Its primitive and lowly organisms with 



Am. Jour. Sci— Third Series, Vol. XXX, No. 1*78.— Oct., 1885. 

 17 



