THE CAUSES OF EARTHQUAKES 



tently brought into existence. In both these periods 

 volcanic activity was pronounced, and beds of coal were 

 formed. When the crust of the earth was crumbling, 

 mountains grew spasmodically (they sprang up, as it 

 were, from out of the giant forces which we have de- 

 scribed earlier in this book) ' faults ' gave rise to earth- 

 quakes, volcanic forces found their vents, and conditions 

 existed which gave rise to the accumulation of materials 

 to form coal."" 



But, the reader will naturally inquire, if " faults " gave 

 rise to earthquakes, and faults are the result of pressure, 

 what produces the pressure ? And what produces the 

 mountains ? Before we answer that we must again have 

 recourse to examples taken from common experience. 

 A sheet of glass or of marble we usually regard as a 

 thing that may break but does not bend. But all of us 

 have seen glass strips, if they are long enough, bend 

 under their own weight ; and there are even marble 

 mantelpieces which, if examined, show that the slab of 

 marble has bent. Thus we can readily imagine that some- 

 times the strata of the earth will bend by reason of the 

 weight put upon them. If that weight is not put on 

 them quite evenly the strata will be still more likely 

 to bend ; it will go from bending to buckling, and from 

 buckling to breaking. As soon as it breaks there will be 

 a "fault" formed. Those who recollect what we have 

 said about the enormous weight of the rocks one above 

 the other will not have to search far for the cause of weight 

 sufficient to bend or buckle the rock strata of the earth. 

 And those who have followed carefully all that has been 



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