270 SEE— FURTHER RESEARCHES ON [April 24, 



Andes Mountains, which are the youngest of the great mountain 

 systems of the globe. 



13. The terrible fracturing of the crust in the sharp folding 

 involved in the formation of the Andes enabled a vast number of 

 volcanoes to break out, and about one hundred and five have been 

 active within historical times. 



14. The formation and activity of the volcanoes in the Aleutian 

 and Japanese Islands is similar to those in the Andes, and represent 

 conditions suitable to the maximum development of volcanic activ- 

 ity. These are sharp folds of the crust near a deep sea from which 

 the expulsion of lava is rapid and violent. 



15. The connection of earthquakes with volcanoes and of both 

 phenomena with the sea is clearly established by the geographical 

 distribution and by the vapor of steam emitted by volcanoes. The 

 nature of the underlying material is shown by the ashes, cinders, 

 pumice and lava forced out by the accumulating subterranean steam 

 pressure. 



16. Earthquakes, however, are the more general, volcanoes the 

 more special phenomena. The mountains are formed by the sea, 

 but only a few of the peaks break out into volcanoes. No volcano 

 long remains active very far from the ocean or other large body of 

 water, because as the lava hardens in the throat of the volcano the 

 supply of steam is inadequate to maintain activity. 



17. If we consider the innumerable islands in the sea, it is evi- 

 dent that they too have been uplifted by earthquakes. Som.etimes 

 the sea bottom near them has been undermined in the process of 

 uplifting, and afterwards sunk down, making an adjacent hole in 

 the bottom, and producing seismic sea waves of the first class, as 

 in mountain formation where trenches are being dug out near the 

 continents. 



18. Seismic sea waves of the second class are produced by the 

 uplift of the sea bottom, into ridges, or submarine plateaus and 

 islands. In such cases the water rises suddenly without previously 

 withdrawing from the shore. 



19. But seismic sea waves of the first class due to the sinking 

 of the sea bottom, after it is undermined by the expulsion of lava, 

 are the most important and most celebrated. The waves at Helike, 



