1906.] 



SEE— THE CAUSE OF EARTHQUAKES. 411 



geological theories regarded the mountains as formed in the past, 

 while it seemed to me that some of the mountains are near enough 

 to the seashore to be still in the process of upheaval. In reflecting 

 over these questions, on May 20th, I recalled, from impressions ob- 

 tained at the Coast Survey in 1899, that some of the islands in the 

 sea had depressions on the side of them as if the material had been 

 thrown up from the adjacent bed, and that deep trenches in the 

 oceans also ran parallel to the great ranges such as the Andes. I 

 noticed also that the volume of the Andes and of the islands were 

 severally not very far from equal to those of the adjacent trough 

 and sinks. Could it be possible that the Andes also had been raised 

 by matter pushed up under the crust from the bed of the adjacent 

 oceanic trough? On recalling that the sea bottom near Pelee has 

 been found by observations to have actually sunk after the great 

 ejection of ashes and vapors in 1902, and that the hollow form of 

 the Andean trough would prevent vertical eruptions from beneath, 

 and cause any explosions which might originate under it to seek 

 release at the sides, thus pushing up the mountains through col- 

 umns or rather layers of lava advanced little by little, by *' lateral 

 thrusts," as the geologists say, from under the sea, I did not hesitate 

 to conclude that the Andes had originated in that way. The ex- 

 istence of the long trough, so deep and so exactly parallel to the 

 mountains for so great a distance, proved it ; and it was easy to see 

 also that later the resistance toward the land side would become so 

 great, owing to the great distance and height of the mountains, that 

 release would eventually come more easily by the other side of the 

 trough folding up into a parallel range, which would thus emerge 

 from the sea as the New Andes, and eventually cause a further re- 

 cession of the west coast line of South America. 



The provisional entertainment and private acceptance of these 

 views seemed daring enough, but it appeared to me there was no 

 escape from them. On the following day. May 21, I recalled that 

 geodetic observations indicated a feebler attraction for mountains 

 than if they were solid and of the same mean density as the crust ; 

 and it was evident that my earlier conception of pumice-filled cones 

 and chains had not been altogether too rash. The rest of the work 

 consisted in nothing but verification and elaboration of these 

 intuitions. 



