550 THE MISSISSIPPI AT NEW ORLEANS. 



feet deep. At the flood state the water rises 50 feet at the 

 mouth of the Red River, but of course retains its level at 

 the Gulf thus giving the head necessary to force forward 

 the increased volume of the discharge.'' * 



We are careful to note this circumstance because it 

 furnishes an explanation of the phenomenon of a re- 

 sistless torrent, flowing" like a mill-race through a dead 

 flat country, such as exists both on the Mississippi and 

 the Ganges during flood time, upon the last section of 

 their respective courses. The Mississippi floods are 

 generally at their highest in April, and the level of 

 the river falls to its lowest point, as a rule, in 

 October. 



Sir Charles Lyell gives a careful and accurately 

 prepared account of the Mississippi, which he visited 

 for purposes of scientific observation, during his geo- 

 logical tour in America, and he states that according 

 to the most recent U.S. Government surveys, the 

 area of its delta is about 12,300 square miles, f 



The average depth of fluviatile formation in this area 

 is supposed to be somewhat more than 500 feet, for 

 in borings made near Lake Pontchartrain, not far from 

 the city of New Orleans, the bottom of the alluvial 

 deposit was said not to have been reached, even at 

 600 feet. This of course goes to show that all this 

 territory has by degrees been built up by the great 

 river, upon what was formerly a deep water area of 

 the Gulf of Mexico, The work of construction is still 

 going on, and year after year the river bar, as we 

 have already explained, is pushed further and further 



* Encycl. Brit., gth Edition, Vol. xvi., p. 520. 



f Principles of Geology, by Sir Chas. Lyell, 1867, Vol. i., p. 458. 



Report of Surveys of 1861, by Messrs. Humphreys and Abbot. 



