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Geo- 







Ch. XIL] 



REVEALED TO US BY GEOLOGY. 



249 



lobe. In every century the land is in some parts raised, 



and in others depressed in level, and so likewise is the bed 

 of the sea. By these and other ceaseless changes, the con- 

 fio-uration of the earth's surface has been remodelled again 

 and again, since it was the habitation of organic beings, and 

 the bed of the ocean has been lifted up to the height of some 



of the loftiest mountains. 



imao 



apt to take 



alarm when called upon to admit the formation of such 

 irregularities in the crust of the earth, after it had once 



time 



allowed, the operation need not subvert the ordinary repose 

 of nature ; and the result is in a general view insignificant, 

 if we consider how 



mountain 



cause our globe to differ from a perfect sphere. Chimborazo, 

 though it rises to more than 21,000 feet above the sea, would 

 be represented, on a globe of about six feet in diameter, by 

 jrain of sand only the twenty-eighth part of an inch in 



thickness. 



may 



The superficial inequalities of the 

 deemed minute in quantity, and their distribution at any 

 particular epoch must be regarded in geology as temporary 



peculiarities, like the height and 



outline of the cone of 



Vesuvius in the interval between two eruptions. But al- 

 though, in reference to the 

 unevenness of the surface is so unimportant, it is on the 



magnitude of the globe, the 



small 



• i • 



that the 



state of the atmospher 



and both the local and general 



man 



Before I insist on the great fluctuations in temperature, 

 to which the ever-varying form of the earth's crust must 

 inevitably give rise, it will be desirable to say something 

 of those geographical changes which are demonstrated 

 by our geological records to have taken place. The reader 

 has been in some degree prepared for the contemplation of 



such revolutions by what we have said in our retrospective 

 survey of former states of the animate creation as bearing on 

 climate. He has been told that even since the commencement 

 of the Glacial Period, when the living species of testacea and 

 most of the existinsr animals and -plants were in being, great 



