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to 







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id i : 





w 





W 



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m 



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•4 



Ch. VII.] 



OF MOUNTAIN-CHAINS. 



135 



of Deville, suffer a contraction of 10 per cent., or whether the 

 sinking be dne to the subtraction of lava driven elsewhere to 

 some volcanic orifice, and there forced outwards or whether 



masses 



it oe urougnu uii uj ^xv «— — o 



during refrigeration, or by the condensation ot gases, or any 

 other imaginable cause, we have no reason to incline to the 



brought 



idea that the consequent geological changes 

 about so suddenly, as that large parts of continents are swal- 

 lowed up at once in unfathomable subterranean abysses, it 

 cavities be formed, they will be enlarged gradually, and as 

 gradually filled. We read, indeed, accounts of engulphed 

 cities and areas of limited extent which have sunk down many 

 yards at once ; but we have as yet no authentic records of 

 the sudden disappearance of mountains, or the submergence 

 or emergence of great islands. On the other hand, the creeps 

 in coal mines* demonstrate that gravitation begins to act as 

 soon as a moderate quantity of matter is removed even at a 

 great depth. The roof sinks in, or the floor of the mine rises, 

 and the bent strata often assume as regularly a curved and 

 crumpled arrangement as that observed on a grander scale 

 in mountain-chains. The absence, indeed, of chaotic disorder, 

 and the regularity of the plications in geological formations 

 of high antiquity, although not unfrequently adduced to 

 prove the unity and instantaneousness of the disturbing 

 force, might with far greater propriety be brought forward 

 as an argument in favour of the successive application of 

 some irresistible but moderated force, such as that which can 

 elevate or depress a continent. 



may 



down thro 



mountain 



force of one kind, namely, that of subterranean movement, 

 while it deprives us of another kind of mechanical force, 



nam 



which the geologist requires for the denudation of land dur- 

 ing its slow upheaval or depression. It may be safely afiirmed 

 that the quantity of igneous and aqueous action — of volcanic 

 eruption and denudation — of subterranean movement and 



* See Ly ell's Elements of Geology, ch. v. p. 50. 



