282 SEE— TEMPERATURE, SECULAR COOLING [April 20, 



causes, but are mainly traceable to the effects of great earthquakes 

 of the present and past, which have left the earth's crust much 

 broken and distorted and often in an unstable condition. 



This is clearly shown by the after-shocks which follow world- 

 shaking earthquakes in great numbers and for a long time. Thus 

 nearly all earthquakes result directly or indirectly from the great 

 earthquakes; but the movement in different cases is doubtless very 

 different, and consists largely in the gradual adjustment of the dis- 

 turbed crust. Hence our principal conclusions are the following: 



1. The cause of world-shaking earthquakes, mountain formation, 

 and kindred phenomena connected with the physics of the earth, is 

 the secular leakage of the ocean bottoms, which gives rise to the 

 development of steam beneath the earth's crust. 



2. This vapor and no other is the cause of these disturbances, 

 because if any other vapor were at work beneath the crust some of it 

 would escape through the vents of volcanoes, and become recog- 

 nizable by observation. 



lowering the level, the crust, having the weight at length removed, would 

 spring upward, perhaps recovering much or all of the elevation lost by 

 denudation. The following considerations will show that this reasoning as 

 applied to geology is likely to be fallacious. Under ordinary conditions 

 denudation is very slow, and the unloading too gradual to produce anything 

 but the most insensible relief upward. We can see that this will be true 

 by considering how little a corresponding increase of load would sag the 

 level. If for example the load be a mass of soil or of rock 100 feet deep, 

 the sagging where the ground is hard, but not solid rock, would be of the 

 order of a few inches. The removal of such a load would no doubt give 

 rise to a similar restitution upward, but no more ; and as such denudation in 

 nature is excessively slow, the springing upward is infinitesimal, and re- 

 quires nearly infinite time. Therefore no important geological effects depend 

 on such causes, though perhaps insensible surface movements may thus arise. 

 But they would scarcely claim the title of microseisms and certainly could 

 not rise to the dignity of earthquakes; for even if landslides should occas- 

 ionally develop in this way the resulting shocks would be mere local tremors. 

 No heavy earthquakes could depend on such causes, for if so they should be 

 observed far inland as well as along the sea coast, which is contrary to obser- 

 vation. Accordingly while such reasoning is learned, and mathematically 

 interesting, it has only a slight physical basis, and as applied to geology is 

 deceptive and misleading. Until the true cause of world shaking earthquakes 

 is placed beyond doubt and fully recognized, the consideration of such infini- 

 tesimal influences as this had better be passed over, because it simply be- 

 wilders the subject. In this connection particular attention is called to the 

 footnote on pp. 408-409 of the paper on the cause of earthquakes. 



