THE BAR -OF THE MISSISSIPPI. 543 



swept away, and become disinfected by infiltration with 

 the earthy particles so thickly suspended in the water. 

 The same remarks hold good with regard to the Amazon, 

 the Indus, and many other great rivers. 



The quantities of sediment carried down to the sea 

 by the Mississippi are something enormous. Observa- 

 tions show that the sedimentary deposits annually carried 

 into the Gulf are equal to a prism one mile square by 

 263 feet thick, besides heavier matters which are pushed 

 along the bottom equal to another square mile 27 feet 

 thick : * so that for many miles from its mouth, the Gulf 

 of Mexico is coloured brown by the river water. The 

 delta of the Mississippi is also perceptibly increasing 

 in size, and the bar at its mouth is estimated to travel 

 out to sen at rates varying from 20 to 100 yards a 

 year, f As new bars are successively formed to sea- 

 ward of the old, the sediment which formed the old 

 one is again lifted up by the current and carried fur- 

 ther out to sea. 



The natural bar of the Mississippi had only 15 feet 

 of water upon it, but this has been increased to 

 30 feet by engineering works, executed by the 

 United States Government since 1875. The rise of the 

 tides, which generally affords such material aid to 

 shipping in the passage of bars, is here unfortunately 

 very small, the vertical rise of spring tides on the S. 

 W. passage being only i Va feet. ** This has therefore 

 always created a great obstruction to navigation, for 



* Encycl. Brit., 9th Edition., Vol. xvi., p. 526 (Art. "Mississippi 

 River ").' 



f The Physical Geography of the Sea, by Lieut. M. F. Maury, 

 U.S.N., i6th Edition, 1877, p. 190. 



Ibid., p. 190. 



** Norie's Navigation, 2 1st Edition. Table xvii, Times of High 

 Water at Spring Tides, p. 354. 



