Ch. VIII.] 



THE OLDER AND NEWER ROCKS. 



145 

















,i 









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1.1 











f v - ' 



■2K 



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** 



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P*oiii°' on and the eruptions of active voleanos, are convinced 

 that great changes are now continually in progress in the 

 interior of the earth's crust far out of sight. They must be 

 conscious, therefore, that the inaccessibility of the regions in 

 which these alterations are taking place, compels them to 

 remain in ignorance of a great part of the working of existing 

 causes, so tha't they can only form vague conjectures in regard 

 to the nature of the products which volcanic heat, aided by 

 steam and other gases, may elaborate under great pressure. 

 But when they find in mountain-chains of high antiquity, 

 that what was once the interior of the earth's crust has since 

 been forced outwards and exposed to view, they will naturally 

 PYT^APf, in ihp Anamination of those mountainous regions, to 



have an opportunity of gratifying their curiosity by obtaining 



remote 



temp 



Having 



mountain-chains some 



rocks of aqueous and volcanic origin, corresponding in cha- 

 racter to superficial formations of modern date, they will 

 regard any other class of ancient rocks, such as granite and 

 gneiss, as the residual phenomena of which they are in search. 

 These latter rocks will not answer the expectations previously 

 formed of their probable nature and texture, unless they wear 



£S of 



having been altered by subterranean heat and gases under 

 great pressure ; in a word, unless they differ wholly from 

 the fossiliferous strata deposited at the surface, or from the 

 lava and scorise thrown out by volcanos in the open air. It 

 is the total distinctness, therefore, of crystalline formations. 



a foreign and mysterious aspect, and bear the mar 



m 



substance of which the origin is familiar to us, that consti- 

 tutes their claim to be regarded as the effects of causes now 

 in action in the subterranean regions. They belong not to 

 an order of things which has passed away ; they are not the 

 monuments of the primeval period, bearing inscribed upon 

 them in obsolete characters the words and phrases of a dead 

 language ; but they teach us that part of the living language 

 of nature, which we cannot learn by our daily intercourse 

 with what passes on the habitable surface. 



VOL. I. 



L 



