300 SEE— THE CAUSE OF EARTHQUAKES. [Octob r 19, 



in this paper any mountain may become a volcano, on short notice, 

 if the internal violence is sufficient to break open an outlet for the 

 vapors which always slumber beneath. We shall see, hereafter, that 

 the mountains are all filled with volcanic materials, and an explosion 

 is all that is required to set them going, and this is usually effected 

 by the throes of an earthquake. All new volcanoes, and old ones 

 when they burst forth into renewed activity, do so with violent 

 earthquake shocks. The shocks of an earthquake almost always have 

 some effect on a burning volcano, and in earthquakes remote from 

 erupting centers, the breaking out of a volcano causes the shocks to 

 cease, as was long ago noticed by Strabo. 



Since this intimate connection has been observed again and 

 again, and the volcanic and earthquake belts are generally similar, 

 though not strictly identical, throughout the world, there is a very 

 strong indication that both depend upon a common cause, and that 

 cause is nothing else than ordinary steam. It is worth while to 

 notice that as Central America is a narrow country, with fairly deep 

 seas on both sides, it is exactly where we should expect volcanic 

 forces to have great sway, and observation shows that this is true 

 for earthquakes as well as volcanoes. The recurrence of frightful 

 earthquakes in that region, and the upheaval of three new volcanoes 

 within historical times speaks for itself, and shows that all the 

 mountains are not yet finished ; and that some of the land in Central 

 America is being elevated by forces depending on the influence of 

 the sea, whether volcanic or seismic. As the result of his observa- 

 tions Darwin held that volcanoes break out in rising areas, most 

 likely because an outlet is easily established when the outer layers 

 are cracked open to a great depth. 



§ 13. The relation of earthquakes to volcanoes. 



In his interesting work on " Earthquakes in the Light of the New 



Seismology," p. 43, Major Dutton follows Professor Milne in his 



classifications, and remarks : 



" Though it is possible to indicate regions which present both Volcanoes 

 and earthquakes, there is no proof of interdependence between seismicity 

 and*vulcanicity in general. While there are earthquakes which are certainly 

 of volcanic origin, the one phenomenon does not necessarily imply the other." 



Professor Milne, Omori, Dutton, and others have recently at- 

 tempted to disprove the relationship of earthquakes and volcanoes 



