190 AGE OF DELTA OF MISSISSIPPI. [CHAP. XXXIV. 



the larger part of that impalpable mud, which constitutes the 

 bulk of the solid matter carried into the sea by the Mississippi, 

 is not lost altogether, so far as the progress of the delta is con 

 cerned. So impalpable is the sediment, and so slowly does it 

 sink, that a glass of water taken from the Mississippi, may 

 remain motionless for three weeks, and yet all the earthy matter 

 will not have reached the bottom. If particles so minute are 

 carried by the current, setting for a great portion of the year 

 from west to east, across the mouth of the river, into the Gulf 

 Stream, and so into the Atlantic, they might easily travel to the 

 banks of Newfoundland before sinking to the bottom ; and some 

 of them, which left the head waters of the Missouri in the 49th 

 degree of north latitude, may, after having gone southward to 

 the Gulf, and then northward to the Great Banks, have found 

 no resting-place before they had wandered for a distance as far 

 as from the pole to the equator, and returned to the very latitude 

 from which they set out. Were it not for the peculiar manner 

 in which the Mississippi forms long bars of sand, which frequently 

 unite with some part of the coast, so as to dam out the sea and 

 form lagoons, the deposition of sediment in the delta would be 

 much less considerable. A lagoon, like Lake Pontchartrain, 

 once formed, becomes a receptacle of the finest mud, poured into 

 it by an arm of the great river during the flood season, and the 

 space thus parted off from the Gulf by bars of sand, is protected 

 from the action of the breakers and marine currents. 



When I inquired what might be the depth of the fluviatile 

 mud in the suburbs of New Orleans, I was told that, in making 

 a railroad near Lake Pontchartrain, piles were driven down sixty 

 feet into the soft mud or slush, and when a boring was made 

 there, 600 feet deep, beds of gnathodon were found, but no 

 marine shells. 



The depth of the alluvium may vary in different parts of the 

 great sloping plain ; for certain areas, such as the &quot; sunk coun 

 try,&quot; for example, west of New Madrid, may have been repeat 

 edly depressed, and have been always brought up again to the 

 same superficial level, by the deposition of the river rnud, or the 

 growth of vegetable matter. 



