318 



CAUSES OF BEEAKS IN 



[Ch. XIV. 



bouring land. But, if the bottom be lowered by sinking at 



same 



never be turned into dry land. In that case one new layer of 



superimpo 



many thousand feet, and the fossils of the inferior beds may 

 differ greatly from those entombed in the uppermost, yet 

 every intermediate gradation may be indicated in the pas- 

 sage from an older to a newer assemblage of species. Grant- 



monumen 



may thus be elaborated in certain parts of the sea, and that 

 the strata happen to be all of them well adapted to preserve 



many 



must still concur before these submarine foi 



laid open to our investigation ! The whole deposit must first 



be raised several thousand feet, in order to bring' into view 



the very foundation; and during the process of exposure 



must 



dation. 



In the first place, the chances are nearly as three to one 

 against the mere emergence of the mass above the waters, 

 because nearly three-fourths of the globe are covered by the 

 ocean. But if it be upheaved and made to constitute part of 



the dry land, it must also, before it car 

 instruction, become part of that area 

 geologists; and this area comprehends 

 tenth of the whole earth. In this i 



surveyed by 



mall 



already explored, and still very imperfectly known, we are 

 required to find a set of strata, originally of limited extent, 

 and probably much lessened by subsequent denudation. 



Yet 



from 



organic world to another, that so many geologists have em- 

 braced the doctrine of great and sudden revolutions in the 

 history of the animate world. Not content with simply 

 availing themselves, for the convenience of classification, of 

 those gaps and chasms which here and there interrupt the 

 continuity of the chronological series, as at present known, 

 they deduce, from the frequency of these breaks in the chain 

 of records, an irregular mode of succession in the events 









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