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GEOGRAPHY, 



16 



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again, we trench on the province of the botanist ; and yet 

 the geographer should inquire how far vegetation extends 



up the 



mountain side, and what 



are the changes which 



it undergoes. How far is it influenced by the change of 

 soil, or the abundance or absence of springs ? Nor can 

 we complete our information respecting a mountain chain, 

 unless we know the len<zth to which it extends, and the 



breadth of country which it covers. 



Valleys are a necessary complement 

 masses, and there are many peculiarities connected with 



to 



aiountam 



• *i 



them well deserving observation. Are the side 



^^ 



preci- 



pitous or sloping ? are they wide or narrov/ ? well watered 

 or arid ? wooded or barren ? Do the rocky sides corre- 

 spond with each other in their salient and re-entering 

 angles ? How far do they extend into the bosom of the 

 mountains? and how are the subordinate vallevs con- 

 nected with the principal one? But there is another 

 peculiarity of valleys not to be lost sight of. There 

 are some which convey to the traveller the impression 

 that ho is passing tlirough a mountainous or hilly country, 

 so steep, rugged, and lofty are the hills by which he is 

 surrounded. It is only on reaching their summit that he 

 becomes aware that the country through which he has 

 been passing is an extensive plain, or table-land, inter- 

 sected by deep chasms and valleys, cut through the soft 

 soil by the constant efforts of the streams by which it is 

 traversed ; such valleys of excavation as these have been 

 sometimes not unaptly called negative valleys. 



3. Bivcrs .—Scarcely less important than that of moun- 

 tains is the effect of rivers in modifviusr the seosra- 



*_-^ 



o"'-& 



phical configuration of a country. From their sources in 





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