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CHAP. XXI. 



On the successive Forms of the Earth : Revolutions 

 of the Globe. 



THE subject of the present chapter is intimately con- 

 nected with a rational theory of the earth. It com- 

 prises the history of those revolutions of the surface, 

 previously to its last, or present, condition, which 

 have, at different times, involved the destruction of 

 some, at least, of the organized beings by which it 

 was inhabited. To these revolutions we are in- 

 debted for its most striking and important features ; 

 as to these it is owing, that the animals of former 

 days are now known to us, and that their vegetables 

 are treasured up for the supply of our wants. If the 

 magnitude of the powers which these changes in- 

 volve, and the undefined ages which they demand, 

 are alarming to those whose views have been con- 

 fined, by timidity or prejudice, to a narrow circle 

 of obvious facts, let them recollect that nature every 

 where displays the marks of enormous power more 

 than once exerted ; and that in the destruction which 

 she every where exhibits, in the equally extensive 

 and tedious successive loss and renewal of races of 

 organized beings, and in many other geological phe- 

 nomena which I need not now enumerate, there is 

 implied the necessity of a duration to which we dare 

 not assign a boundary. 



In preceding chapters, the nature and the ap- 

 pearances of strata and of stratification, the changes 

 of position which these have undergone, and the 

 sources of the unstratified rocks, have been so far 

 explained, as to enable the reader to follow without 



