PHYSICAL GEOGEAPHY. xxiii 



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great lakes separate it towards tlie north and north-east from 

 the latter, and from the basin of the St. Lawrence, leaving a^ 

 triangle scarcely larger than France to supply the great 

 tributaries of the Ohio Hiver. 



The Western third — that is, of the country between the 

 Pacific Ocean and the Eocky Mountains — is so cut up by 

 mountains, that we shall leave the consideration of its 

 drainage for the present. 



The physical geography of the Western two-thii-ds, which 

 • consists of the country west of the Mississippi, is peculiar, 

 ^althougli by no means complicatedj and will exclnsiyely 

 ^occupy our attention. 



I will first indicate tlie general rise of these regions^ from 

 the Mississippi on the east and the Pacific on the Avest, to 

 ^ / their lofty central eleyations^ and then discuss the several 



mountain systems which have been upheaved by forces very 

 *** - different, both in de«;ree and mode of action, from those which 

 ^>* ■ uniformly raised the entire country from its bases to its centre. 



From the Gulf of Mexico, where the elevation is nil, passing 

 northward up the Mississippi, we do not rise more than 470 

 feet during the 1,202 miles from the mouth of the river to 

 St. Louis. 



During the next 730 miles, up to St. Paul, the rise' is 

 ' " again nearly 470 feet. The falls of Sf. Anthony, nineteen 



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i^miles above St. Paul's, are the limit to which continuous 



n pteam navigation at present extends, the total distance being 



""l,952 miles. 

 ^ A hundred miles further up stream the elevation is found to 

 ^•e 1,152 feet, which is not much below that of the little lakes 

 10^ . j; 'om which the head-waters rise. Lake Superior lies from 



.-.hj to a hundred miles only to the east of these lakes, and 



jiiis an elevation of 600 feet, while the land intervening, which 



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