[ 165 ] 



No. 



Description of the river Mississippi and its Delta, with that of the 

 adjacent parts of Louisiana. By William Dunbar, of the Nat- 

 chez, communicated by the Author, a Member of the Society; 

 through the President. 



Read April 6th, 1804. 



THE multiplicity of the rivers which are tributary to the 

 Mississippi, extending themselves over an immense tract which 

 comprehends nearly 20°. in hit. and 30°. in long, must render 

 this river, at all seasons, one of the most considerable on the 

 globe. The annual inundation, being supplied from so great a 

 variety of climates, must naturally be expected to be of long 

 duration; and may generally be estimated at nearly half the 

 year; beginning (com. annis) to rise in January, and fall in 

 June; the two extremes being frequently extended by the 

 early autumnal and winter rains in the southern latitudes, and 

 by the protraction of the northern winters, which retards the 

 dissolution of the immense accumulations of snow in those 

 cold regions. At the landing of the Natchez (380 miles from 

 the mouth of the river) the perpendicular ascent of the waters 

 of the Mississippi, from the lowest ebb to the highest inunda- 

 tion, may be estimated at 50 feet. At Baton Rouge (200 miles 

 distant) it was found to be 30 feet; at New-Orleans (80 miles 

 above the mouth) it is about 12 feet; and at the mouth of 

 the river, scarcely any perceptible change is observed, except- 

 ing by a stronger current charged with earthy matter rolling 

 into the ocean during the season of the inundation; at which 

 time, all the lakes and communications with the sea are re- 

 plenished with the waters of the inundation, and the ocean 

 itself is often repelled to such a degree, that fresh water has 

 been drawn up, out of sight of land. This great difference in 

 the perpendicular rise of the waters of the inundation is to be 

 accounted for from the prodigious number of natural canals 

 issuing from the Mississippi, and those immense bluets of water, 



