354 SEE— THE CAUSE OF EARTHQUAKES. [October 19, 



trations of the principle may be readily found, and must convince 

 even the most sceptical of its general validity. 



If we apply this principle to Guam, the Philippines, the Aleutian 

 Islands, Puerto Rico and other islands of the Antilles, we shall be 

 able to explain how the mountains of these countries have been 

 raised, and the islands themselves developed by matter injected from 

 under the troughs near them.^ This seems to remove all doubt as 

 to the process involved in the formation of islands, and the smaller 

 land areas, and we may consider the plains and slopes of the larger 

 land areas bordering on the sea. 



If the injections are powerful, as in South America, the up- 

 heaval of matter by the power of steam brings the subsidence of the 

 adjacent bottom and the accompanying sea waves. We need not 

 assume, and we do not assume, any original weakness or line of 

 weakness of the earth's crust, but simply that the ocean bed leaks, 

 and the steam pressure tends to heave it up, and that the process 

 works at various depths from ten to twenty miles, and is continued 

 at irregular intervals over long periods. 



This principle of ridges enables us to understand why islands 

 rise from the sea in chains — in such cases they are really submerged 

 and perhaps immature mountains. The Aleutian Islands are now in 

 this state, and many others may be pointed out. When a ridge is 

 once started, the chances greatly favor another parallel to the first, 

 because of the way the sea bottom is depressed nearby, in forcing 

 up the islands from beneath. 



If we examine relief maps of the world,- we shall see by the 

 mountains parallel to the shores exactly where the ocean used to be 

 and how it gradually withdrew. Thus, the successive ridges of the 



^ As throwing light upon some remarkable processes of stability in nature, 

 it is interesting to notice that when a volcanic cone has been upheaved in 

 the sea, and by successive uplifts raised above the water to become an island, 

 the s.ubsidence that eventually takes place, after much matter has been ex- 

 pelled from beneath the crust to make the island, does not appreciably en- 

 danger the island itself, which is powerfully braced by the conical form of 

 its base. When a portion of the sea bottom sinks near by, to partially fill up 

 the cavities in the crust, the settlement of the bed of the ocean scarcely dis- 

 turbs the island, on account of the way in which the crust is upraised about 

 its base, and braces it on all sides. 



'Those of Rand, McNally & Co., given in the Encyclopcudia Americana, 

 have been found extremely useful. 



