140 



CHAPTEE VIII. 



DIFFERENCE IN TEXTURE OF THE OLDER AND NEWER ROCKS. 



CONSOLIDATION OF FOSSILIFEROUS STRATA SOME DEPOSITS ORIGINALLY SOLID 



TRANSITION AND SLATY TEXTURE CRYSTALLINE CHARACTER OF PLUTONIC 



AND METAMORPHIC ROCKS — THEORY OF THEIR ORIGIN— ESSENTIALLY SUB- 

 TERRANEAN — NO PROOFS THAT THEY' "WERE PRODUCED MORE ABUNDANTLY AT 

 REMOTE PERIODS. 



Another 



argument in favour of the dissimilarity of the 



causes operating at remote and recent eras lias been derived 

 by many geologists from tlie more compact, stony, and 

 crystalline texture of the older as compared to the newer 

 rocks. 



>/ 



— This subject may be considered, 



first, in reference to the fossiliferous strata ; and, secondly, 

 in reference to those crystalline and stratified rocks which 

 contain no organic remains, such as gneiss and mica-schist. 

 There can be no doubt that the former of these classes, or 

 the fossiliferous, are generally more compact and stony in 

 proportion as they are more ancient. It is also certain that 

 a great part of them were originally in a soft and incoherent 

 state, and that they have been since consolidated. Thus we 

 find occasionally that shingle and sand have been aggluti- 

 nated firmly together by a ferruginous or siliceous cement, or 

 that lime in solution has been introduced, so as to bind toge- 

 ther materials previously incoherent. Organic remains have 

 sometimes suffered a singular transformation, as, for example? 

 where shells, corals, and wood are silicified, their calcareous 

 or ligneous matter having been replaced by nearly pure 

 silica. The constituents of some beds have probably set and 

 become hard for the first time when they emerged from 

 beneath the water. 







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