igoS.] THE PHYSICS OF THE EARTH. 261 



in time the movements may give rise to neighboring islands. All 

 of these considerations show the value of accurate knowledge of the 

 sea bottom at this epoch. 



§ 53. Greatness of the Forces zvhich Uplift and fold the Earth's 

 Crust. — The tremendous power of earthquake and volcanic forces 

 has been proverbial from the earliest ages of history, and finds 

 expression also in the universal terror thus excited among all liv- 

 ing beings. This extreme terror is only too well justified by the 

 vast extent of the ruin too often wrought in dififerent parts of the 

 world. But probably only those who have witnessed a great earth- 

 quake can adequately appreciate the awful character of the com- 

 motion, and the gigantic forces which must underly it. This is 

 shown also by the many published attempts to belittle the signifi- 

 cance of earthquake disasters. 



Some writers of eminent mathematical learning, but apparently 

 lacking in grasp of the larger physical phenomena, have ascribed 

 earthquakes to inequalities of loading, changes of barometric pres- 

 sure, etc., and have with strange and almost marvelous credulity 

 believed that the settlements of the earth thus arising would shake 

 down cities and devastate whole countries. How these learned 

 authorities imagined that small subsidences under the steady action 

 of these infinitesimal forces could bring about such long con- 

 tinued shaking and proportionately great havoc is difficult to un- 

 derstand. If the forces are so small, and act so slowly, is it 

 conceivable that the yielding could be anything else than gradual 

 and insensible? Such minute settlements evidently would be like 

 those now experienced in dry inland regions free from real earth- 

 quakes. 



The titanic nature of the forces which have uplifted islands, 

 mountains, plateaus and continents, can scarcely be realized ; yet 

 even the ancients grasped it to some extent when they described 

 the whole region between Naples and Sicily as underlaid by a giant, 

 whose movements disturbed the intervening sea bottom. In his 

 account of the Chilean earthquake of 1835, Charles Darwin showed 

 that the entire region from the island of San Fernandez to the 

 Andes, about 450 miles across, had been moved together by under- 

 Iving forces. " There was undoubtedlv a connection between the 



