Earthquakes and Volcanoes 



ten feet above high- water mark; and an exten- 

 sive rocky flat, previously covered by the sea, 

 was exposed as dry land. In like manner, the 

 bottom of the surrounding sea must have been 

 elevated, for soundings all round the island be- 

 came shallower by about nine feet. It is true, 

 there was a partial subsidence shortly afterwards, 

 but this was far from sufficient to neutralize the 

 upheaval, and the net result showed a permanent 

 elevation. It is considered probable, that the 

 greater part of the South American coast has, 

 been raised several hundred feet by a succession 

 of such small upheavals. 



When an area is thus raised, the addition sud- 

 denly made to the mass of dry land may be very 

 considerable, and will compensate for the effects 

 of denudation continued through a long period. 

 It was calculated, for example, by Sir C. Lyell, 

 that, during an earthquake which occurred in 

 Chile in 1822, a mass of rock more than equal in 

 weight to a hundred thousand of the great 

 pyramids of Egypt was added to the South 

 American continent. If a single convulsion of 

 this kind can thus raise such an amount of solid 

 land from beneath the waters, it is obvious that 

 these movements must be of great service in 

 renovating the surface of the earth, and in bring- 

 ing new material within reach of the ever-active 

 agents of denudation. It is proper to remark, 

 that an earthquake-wave is a vibration of the 

 solid crust of the earth, which may, and con- 

 stantly does, occur, without giving rise to any 

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