i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 351 



Aleutian Islands, off the coast of Peru and Chili, near St. Paul's 

 Island in the Atlantic, the Antilles and »the East Indies. And 

 while the investigation of these phenomena is still in its infancy, 

 we may be sure they are of wide and universal distribution, espe- 

 cially in the deepest oceans, where the shores are steep and broken, 

 as in volcanic regions. The southern Pacific Ocean, where so 

 many volcanic islands exist, must be a prolific but unexplored 

 center of such disturbances. 



§ 31. Views of Charles Darzvin on the distribution of volcanic 

 islands. 



" During my investigations on coral reefs, I had occasion to consult the 

 works of many voyagers, and I was invariably struck with the fact that with 

 rare exceptions, the innumerable islands scattered throughout the Pacific, 

 Indian, and Atlantic Oceans, were composed either of volcanic or of 

 modern coral-rocks. It would be tedious to give a long catalogue of all 

 the volcanic islands, but the exceptions I have found are easily enumerated : 

 In the x\tlantic we have St. Paul's Rock, described in this volume, and the 

 Falkland Islands, composed of quartz and clay slate; but these latter 

 islands are of considerable size, and lie not very far from the South iVmer- 

 ican coast : in the Indian Ocean, the Seychelles (situated in a line prolonged 

 from Madagascar) consists of granite and quartz : in the Pacific Ocean, New 

 Caledonia, an island of large size, belongs (as far as is known) to the 

 primary class. New Zealand, which contains much volcanic rock and some 

 active volcanoes, from its size cannot be classed with the small islands, 

 which we are now considering. The presence of a small quantity of non- 

 volcanic rock as of clay slate on three of the Azores, or of the tertiary lime- 

 stone of Maderia, or of clay-slate at Chatham Island in the Pacific, or of 

 lignite at Kerguelen land, ought not to exclude such islands or achipelagoes, 

 if formed chiefly of erupted matter, from the volcanic class. 



" The composition of the numerous islands scattered through the great 

 oceans with such rare exceptions volcanic, is evidently an extension of that 

 law, and the effect of the same causes, whether chemical or mechanical, from 

 which it results, that a vast majority of the valcanoes now in action stand 

 either as islands in the sea, or near its shores. This fact of the oceanic is- 

 lands being so generally volcanic is also interesting in relation to the nature 

 of the mountain-chains on our continents, which are comparatively seldom 

 volcanic ; and yet we are led to suppose that where our continents now 

 stand an oceap once extended. Do volcanic eruptions, we may ask, reach 

 the surface more readily through fissures formed during the first stages of the 

 conversion of the bed of the ocean into a tract of land?"^ 



In connection with the above views of Darwin it should be noted 

 that not all of the islands which are upheaved in the sea could be 



* " Geological Observations on Volcanic Islands," chapter VI. 



