THE CAUSES QF EARTHQUAKES 



has endeavoured to show that all the great convulsions 

 of the earth have their origin in one or other of these 

 areas where usually a great mountain range slopes 

 steeply down to the sea. There are eleven such world- 

 earthquake districts. There is the Alaskan region, 

 where on the shore Mount Elias rises to a height of 

 18,000 feet and where the water is 7000 feet deep sixty 

 miles from the shore altogether a drop of 25,000 feet 

 from the top of the mountain to the bed of the ocean 

 in 200 miles. This drop, without going into measure- 

 ments, may be taken as typical of the rest, which are 

 classified as the Cordillerean region, the Antillean region (in 

 the earthquake district of which Mount Pelee at Martinique 

 and the Soufriere in St. Vincent are situated) ; the Andean 

 district ; the Japan district ; the Javan district ; the 

 Mauritius district ; the Antarctic district ; three sub- 

 marine districts of sunken ridges in the North-Eastern 

 Atlantic, the North- Western Atlantic, and the Northern 

 Atlantic ; and one great land district, distant from the 

 sea, which lumps together all the mountains of the Alps, 

 the Balkans, the Caucasus, and the Himalayas. In thir- 

 teen years, from the time in which earthquake investigation 

 has become a science, 750 great earthquakes originated in 

 these districts. On the average, about sixty great earth- 

 quakes occur every year, or a little more than one a 

 week. In addition to these world-shaking effects there 

 are about 30,000 small earthquakes every year, England's 

 annual contribution to this number being about half 

 a dozen. 



What is the meaning of a "great earthquake," and 



172 



