506 SEE— ORIGIN OF HIMALAYA MOUNTAINS. [April 18, 



The previous illustrations show the city of Arica before this earth- 

 quake, and the mere wreckage which remained after the innunda- 

 tion of the sea. 



In an earlier passage than that above cited, Proctor quotes the 

 description of an eye witness, which tells of the movements of the 

 ships : 



" The agent of the Pacific Steam Navigation Company, whose house 

 had been destroyed by the earth-shock, saw the great sea-wave while he was 

 flying towards the hills. He writes : ' While passing towards the hills, with 

 the earth shaking, a great cry went up to heaven. The sea had retired. On 

 clearing the town, I looked back and saw that the vessels were being carried 

 irresistibly seawards. In a few minutes the sea stopped, and then arose a 

 mighty wave fifty feet high, and came in with a fearful rush, carrying every- 

 thing before it in terrible majesty. The whole of the shipping came back, 

 speeding towards inevitable doom. In a few minutes all was completed — 

 every vessel was either on shore or bottom upwards.' " 



6. Pratt's Reasoning on the Density of the Matter Under 

 THE Ocean, Plains and Mountains, and its Applica- 

 tion to India and the Himalayas. 

 Pratt's reasoning in regard to the density of the matter in and 

 beneath the crust of the earth, and its bearing on the new theory of 

 earthquakes is described in my paper on " The Cause of Earth- 

 quakes, Mountain Formation and Kindred Phenomena Connected 

 with the Physics of the Earth," published in the Proceedings of this 

 Society for 1906, pp. 344-346. His main conclusion is stated thus : 



"This (deflection of the plumb line) shows that the effect of variations 

 of density in the crust must be very great in order to bring about this near 

 compensation. In fact the density of the crust beneath the mountains must 

 be less than that below the plains, and still less than that below the ocean- 

 bed" (Pratt, "Figure of the Earth," 3d edition, Art. 137, pp. 134-135). 



Again : 



" The conclusion at which we have arrived in Art. 137, that the parts of 

 the crust below the more elevated regions are of less density, and the parts 

 beneath the depressed regions in the ocean are of greater density than the 

 average portions of the surface, seems to bear additional testimony to the 

 fluid theory. For it shows that notwithstanding the varied surface, seen at 

 present in mountains and oceans, the amount of matter in a vertical prism 



