386 SEE— THE NEW THEORY OF EARTHQUAKES [November 15. 



crusted state of the earth we must reject the whole doctrine of 

 secular shrinkage as false and misleading. 



As the earth was once of larger volume and smaller density 

 than at present, there may have been a time when it was settling 

 owing to gravitational instability, but this was long before the 

 surface had become encrusted. Since the consolidation began the 

 cooling has been excessively slow, and no convective circulation has 

 taken place within ; consequently the planet has not since experienced 

 any sensible gravitational instability, except that due to earthquakes 

 arising from the penetration of water vapor, which gives rise to 

 mountain formation and kindred phenomena now witnessed at the 

 surface of the earth. The theory of gravitational instability as 

 applied to the earth therefore is not valid, because it applies to a 

 far earlier stage in our history, before the crust had begun to 

 form. The premise underlying this learned reasoning seems there- 

 fore false, and we can only look upon such an ingenious speculation 

 as an interesting example of brilliant abstract reasoning, in no way 

 applicable to the present or recent history of our planet. By no 

 possibility could such theories enable us to explain the distribution 

 of earthquakes, or their prevalence near deep seas, where trenches 

 are being dug out in the sea bottom and mountains uplifted along 

 the borders of these abysses. 



What is said here in regard to these several investigations ap- 

 plies also to Professor Love's learned discussion of the gravitational 

 instability of the earth, involving the various orders of spherical 

 harmonics. His beautiful mathematical theory is a monument of 

 ingenuity, correct on the hypothesis, but the latter is lacking in 

 physical basis, and consequently the investigation is chiefly valuable 

 as a piece of abstract reasoning of high order, interesting in dy- 

 namics, but not applicable to the development of our actual earth. 



§ 13. Views of the Late Professor James D. Dana on Mountain 

 Formation. — Among the many eminent geologists who have treated 

 of mountain formation, the late Professor James D. Dana stands 

 preeminent for having come nearest to the correct theory; and 

 although the false hypothesis of the contraction of the earth under- 

 lies his views and vitiates them, yet they are sufficiently remarkable 



