t907-] 



AND CONTRACTION OF THE EARTH. 281 



VI. Conclusions. "" 



It now remains to sum up very briefly the chief conclusions at 

 which we have arrived. Different arguments appeal with unequal 

 force to different minds, and doubtless there are some who will hesi- 

 tate at departing from the views recently current in the sciences 

 which deal with the earth. Others who have more or less despaired 

 of definite results under the uncertainty and confusion heretofore 

 existing, will naturally be slow to believe that the laws and order of 

 nature are so simple. But these varieties of temperament will not 

 change the force of the several arguments for a single cause shown 

 to underly the most varied phenomena. 



We have endeavored to show not only that the cause assigned in 

 the paper on earthquakes is adequate to account for the observed 

 phenomena, but also, through the process of exclusion, that no other 

 possible cause is at work in world-shaking earthquakes. In this 

 survey of the whole field we were led to reject the theory of contrac- 

 tion and secular cooling as an effective agency in modifying the sur- 

 face of the earth. And we contrasted the absence of world-shaking 

 earthquakes in an inland region like Colorado and Kansas or the 

 Desert of Sahara with their constant occurrence along the Andes, as 

 a proof that the forces involved depend on the ocean and not at all 

 on secular cooling. For if this latter is a real cause it should be at 

 work inland as well as along the sea coasts. These considerations 

 therefore seem to establish the cause which has formed mountains, 

 and wrinkled the earth's crust in a very complicated manner. 



In the study of this question consideration was carefully restricted 

 to earthquakes of the world-shaking class, because the great disturb- 

 ances were held to be best adapted to disclosing the true nature of the 

 processes hidden beneath the earth's surface. The problem was 

 thus simplified and cleared of the confusion that would necessarily 

 have resulted from the simultaneous consideration of all earthquakes, 

 both large and small. ^ The slight shocks may be due to various 



^Viewing the earth as an elastic solid under stresses of varying inten- 

 sity several eminent mathematical physicists have recently considered the 

 dilatational stability, or the stability of the crust under its own gravitation, 

 when some of the surface matter is removed. After calculating these hypo- 

 thetical effects by elegant mathematical methods, some of them have in- 

 ferred that when denudation takes place under geological agencies, thus 



