,9o6.] SEE THE CAUSE OF EARTHQUAKES. 305 



examining a relief cast of the Atlantic Ocean exhibited in the office 

 of the United States Coast and Geodetic Survey at Washington, and 

 remarked that it seemed as if the volumes of the upraised islands 

 were not very much larger than those of the adjacent depressions. 

 Why should depressions exist so near these elevations above the 

 sea, and, in the case of mountain ranges, so nearly parallel to them 

 for long distances? Is there not obviously a direct connection be- 

 tween the elevated land and the unusual depression in the adjacent 

 sea bottom? 



To understand just what this connection is, we may recall that 

 after the great eruption of Mt. Pelee in 1902, it was found by actual 

 measurement that a considerable portion of the adjacent sea bottom 



Vertical Section perpendicular to the Andes and Andean trough, drawn to 

 natural scale, and showing the mode of operation of the trough in the 

 formation of mountain and cordilleras. 



had sunk down hundreds of fathoms,^ It is impossible to be- 

 lieve that this settling of the bottom of the sea could be due to the 



^This statement is perhaps somewhat too positive, for Dr. O .H. Titt- 

 man, superintendent of the U. S. Coast Survey, informs me that reHable 

 determinations of depth before the eruption of Pelee seems to have been 

 insufficient to decide the question satisfactorily. The cables were broken, 

 and the subject investigated by the French Commission (Lacroix, Alf, La 

 Montague Pelee et ses eruptions, Paris, 1904), which includes M. Rollet de 

 risle's investigation of the reported changes of depth in the vicinity of Mar- 

 tinique. The French commission "was inclined to ascribe the disturbances to 

 submarine volcanic action, rather than to subsidences. This, however, is not 

 a matter of great importance ; for in his work on " Seismology," p. 35-36, 

 Professor Milne mentions several well established cases of subsidences in 

 the Mediterranean and in the Pacific Ocean off the Esmeralda River in 

 Ecuador. He points out that " disturbances originating beneath the sea, 

 which are much more numerous than those originating beneath the land, 

 likewise emanate from a region of strain. Mr. W. G. Forster, who has 

 paid so much attention to the earthquakes of the Mediterranean, tells us 

 that they have been accompanied by great subsidences of the sea bottom." 



