i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 413 



In certain respects the theory here outlined may be capable of 

 observational tests. The importance of the subject would appear 

 to be such that it may be worthy of consideration whether geodetic 

 investigators of the different nations might not advantageously 

 arrange to establish earthquake and tidal observatories and more 

 precise levels on coasts such as those of Chili, Peru, California, Japan, 

 Italy, Greece and other countries, for the more exact study of pro- 

 gressive secular movements. Has not the time come to test geo- 

 logical and seismological theories by the accumulation of exact 

 empirical data, and is not this a debt which we of this generation 

 owe to the future ? 



§ 65. Seismic activity a maximum along the coasts of deep seas 

 and a minimum in the great inland deserts. 



If the cause assigned for the explanation of earthquakes be 

 confirmed by time and experience, it is evident that no place on 

 the earth can be said to be wholly removed from the danger of these 

 disturbances ; yet the dangers will be a maximum on the coasts of 

 deep seas where the shores are of leaky character and the troughs 

 are at work,^ and grow less and less along the coasts of the shallower 

 waters where the troughs are absent and the stratification of the 

 rocks is more secure. Thus northern and central Europe and the 

 eastern coast of the United States are comparatively safe. Yet 

 sooner or later, but fortunately to be reckoned in many cases by 

 intervals of thousands of years, every place (except the great in- 

 land deserts which are nearly uninhabitable) is likely to be shaken 

 by an earthquake of considerable severity ; and those works of man 

 which are to be preserved and to stand through the centuries should 

 be built accordingly.^ The great layer of water covering the earth, 



^ In his thoughtful article on " Geology," Encyc. Brit., p. 255, Sir Archibald 

 Geikie justly remarks: " Some of the most terrible earthquakes within human 

 experience have been those which have affected the western seaboard of South 

 America." The cause of this is now plain, viz., the Andean Trough is 

 probably the largest and most powerful in the world. And in general the 

 seimicity of a region in the production of world-shaking earthquakes depends 

 on the extent and power of its ocean troughs. 



" Humboldt laments the destruction wrought by earthquakes upon works 

 of art, architecture, monuments and inscriptions of the classic period, which 

 were developed in a region of such high seismic activity as to render their 

 preservation difficult. 



