THE CAUSE OF EARTHQUAKES. 295 



admitted that high winds exert enormous pressures upon 

 moimtain ranges, and might occasionally give rise to 

 stresses causing rocky masses in unstable equilibrium to 

 give way, the coincidences which have been established 

 between the occurrence of storms and earthquakes can 

 usually only be regarded as occurrences which have 

 synchronised by chance. 



Storms are usually accompanied with a barometric 

 depression, and the relation of diminutions in atmo- 

 spheric pressure to earthquakes has been discussed. 



Rain and earthquakes. — It has already been shown 

 that earthquakes have occasionally been found to coin- 

 cide with rain and rainy seasons. Whether the saturation 

 of the ground with moisture or the percolation of the 

 same to volcanic foci may be a direct effect producing 

 earthquakes it is difficult to say. The probability, 

 however, is that, rain being dependent on phenomena 

 like changes in temperature, barometric fluctuations, and 

 winds, we must regard it and the earthquakes which 

 happen to coincide with these precipitations of moisture 

 as congruent effects of more general causes. 



Conclusion, — Although it would be an easy matter to 

 discuss the relationship of earthquakes and other pheno- 

 mena, we must conclude that the primary cause of 

 earthquakes is endogenous to our earth, and that 

 exogenous phenomena, like the attraction of the sun and 

 moon and barometric fluctuations, play but a small part 

 in the actual production of these phenomena, their 

 greatest effect being to cause a slight preponderance in the 

 number of earthquakes at particular seasons. They may, 

 therefore, sometimes be regarded as final causes. The 

 majority of earthquakes are due to explosive efforts at 

 volcanic foci. The greater number of these explosions 

 take place beneath the sea, and are probably due to the 



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