276 EARTHQUAKES. 



of energy, or on the varying sorts and degrees of resist- 

 ance opposed to them.'* 



Although we have many examples of earthquakes 

 having occurred without volcanic eruptions, and, on the 

 other hand, of volcanic eruptions without earthquakes, 

 volcanoes may still be regarded as ' safety-valves of the 

 earth's crust,' which, by giving relief to internal stresses, 

 guard us against the effects of earthquakes. 



That many earthquakes are felt at Copiapo is at- 

 tributed to the fact that in the neighbouring mountains 

 there are no volcanic vents. 



We must not, however, overrate the protective in- 

 fluence of volcanoes. In the Sandwich Islands we see 

 the columns of liquid lava in neighbouring mountains 

 standing at different heights, indicating a want of sub- 

 terranean connection between these vents. In conse- 

 quence of this it would seem that enormous pressures 

 might be generated in the neighbourhood of one of these 

 mountains without finding relief at the other. When we 

 have conditions like these, it would seem that the erup- 

 tion of a volcano may have little or no influence in pro- 

 tecting neighbouring districts. 



This may possibly be the explanation of the fact that 

 in 1835 Concepcion was destroyed, notwithstanding there 

 being an unusual activity in the volcanic vents of the 

 neighbouring mountains. 



1 Mallet, Rejwrt to Brit. Ass., 1858, p. 67. 



