MISSISSIPPI VALLEY. 165 



altitude of 1,490 feet above the sea, to Balize, on the Gulf 

 of Mexico, has been estimated by Schoolcraft at 3,160 

 statute miles, following its windings, and may be stated in 

 round numbers at 2,400 geographical miles in a straight 

 line. The moderate hills and. eminences of the country in 

 which the river has its origin do not rise above the plane 

 of the general eastern slope of the continent in the same 

 parallel ; and the general longitudinal descent of the great 

 valley from Lake Itasca is at the rate of 10 inches in the 

 mile for the upper half of the river, and for the other half 

 of the way, or from St. Louis downwards, of only two 

 inches and a half per mile. 



As St. Louis is 500 feet above the sea, and about 600 

 geographical miles distant transversely from the western 

 summit of the prairie slope (which has been taken at 

 2,500 feet above the sea), the lateral descent of the 

 valley to the channel of the river in that parallel is 40 

 inches in the mile ; but the sinuosities of the Missouri, a 

 mightier stream than the one in which it loses its name, 

 and of the other grand affluents of the Mississippi that 

 drain the prairies, give a gentler inclination to their beds. 

 The Illinois, Ohio, and the minor streams which come in 

 from the other side of the valley, flow at a lower level 

 than the western feeders ; their upper branches being sub- 

 ordinate to the general slope, which has there descended 

 considerably.* 



* The following facts, ascertained at the Navy Yard of Memphis, 

 in Tennessee, by R. A. Marr, Esq., are interesting points in the 

 history of the Mississippi. The quantity of water passing through 

 the channel of the river at that place in 1849 was sufficient to cover 

 an area of 100,000 square miles to the depth of seven feet and a half, 

 and the quantity of silt it carried down would make a bed of earth 

 one mile square and seventy-six feet deep. The current in the 



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