



* 





* 











Ml 



:: 



:■: 





. 







• - - 





. 



- * 





n 







- 





* .* 





% ■ 





Ch. VII.] 



OF MOUNTAIN-CHAINS. 



137 



appreciable to the naturalist, still it is certainly far less 



manifest 



ganic world. Every year some volcanic eruptions take place, 



number 



feet of lava and scoria poured or cast out of various craters. 

 The amount of mud and sand deposited in deltas, and the 

 advance of new land upon the sea, or the annual retreat of 

 wasting sea-cliffs, are changes the minimum amount of which 

 might be roughly estimated. The quantity of land raised 



mie 



computed, and the change arising from such movements in 

 a century might be conjectured. Suppose the average rise 



of the land in some parts of Scandinavia to be as much 

 five feet in a hundred years, the present sea-coast might be 

 uplifted 700 feet in fourteen thousand years ; but we should 

 have no reason to anticipate, from 

 hitherto acquired, that the molluscous fauna of the northern 

 seas would in that lapse of years undergo any sensible amount 



anv zoological data 



of variation. 



Norway 



high, in which the shells are identical with those now living, 

 although their geographical distribution has somewhat al- 

 tered, the fossil species constituting an assemblage which at 

 present characterises the sea several degrees farther north. 

 The rise of land in Scandinavia, however insensible to the 

 inhabitants, has evidently been rapid when compared to the 

 rate of contemporaneous change in the testaceous fauna of 

 the German Ocean. Were we to wait, therefore, till the 

 mollusca shall have undergone as much alteration as they 

 underwent between any two of the twelve larger groups from 

 the Laurentian to the Pliocene enumerated in the table at 

 the end of this chapter, or even in the time intervening be- 

 tween the minor subdivisions of some of these groups, such 

 as the eight ascribed to the Jurassic • or the six into which 

 the Cretaceous are there divided, what stupendous revolutions 

 in physical geography ought we not to expect, and how 

 many mountain-chains might not be produced by the repe- 



moi? 



even perceptible to man ! 



dom 



