270 EARTHQUAKES. 



CHAPTEE XVI. 



RELATION OF SEISMIC TO VOLCANIC PHENOMENA. 



Want of synchronism between earthquakes and volcanic eruptions — 

 Synchronism between earthquakes and volcanic eruptions — Con- 

 clusion. 



Connection between earthquakes and volcanic erup- 

 tions. — Insomucli as it is a recognised fact that regions 

 which are characterised by their seismic activity are 

 chiefly those which are also characterised by the- number 

 of their volcanoes, it is generally assumed that these two 

 phenomena have an intimate relation. The residents in 

 a volcanic country, when seeking for the origin of an 

 earthquake, invariably turn towards the volcanoes which 

 surround them. If a neighbouring volcano is in a state 

 of activity, it is often regarded as a safeguard against 

 seismic convulsions, in other cases it is looked upon as 

 being the cause of such disturbances. In certain in- 

 stances both of these views have apparently been corro- 

 borated. When we consider that an earthquake and a 

 volcanic eruption may both be the result of some great 

 internal convulsion, and that first one and then the other 

 may take place in the same neighbourhood, it is natural 

 to expect that when these internal forces have expended 

 themselves in the production of one of these phenomena, 

 it is not so likely that they should exhibit themselves in 

 the other. The inhabitants of Sicily and Naples, we are 



