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SIR CHARLES LYELL 



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

 the same rate that it is raised by fluviatile mud, the bay can 

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

 matter may be superimposed upon another for a thickness of 

 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- 

 ing, however, that such an unbroken sequence of monuments 

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

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

 the included fossils from decomposition, how many accidents 

 must still concur before these submarine formations will be 

 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 

 the superior beds must not be entirely swept away by denu- 

 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 can be available for our 

 instruction, become part of that area already surveyed by 

 geologists. In this small fraction of land already explored, 

 and still very imperfectly known, we are required to find a 

 set of strata deposited under peculiar conditions, and which, 

 having been originally of limited extent, would have been 

 probably much lessened by subsequent denudation. 



Yet it is precisely because we do not encounter at every 

 step the evidence of such gradations from one state of the 

 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 

 themselves, both in the organic and inorganic world. But, 



