47 

 Notes on the Delta of the Mississippi River. 



William A. McBeth. 



The large scale map of the Alluvial Valley of the Lower Mississippi 

 River published by the Mississippi River Commission, St. Louis, Mo., is a 

 fine example of map making and a most valuable adjunct to geography 

 study in the public high schools and colleges. 



A study of this map reveals many interesting facts related to the 

 growth of the delta that the stream has formed in the edge of the Gulf 

 of Mexico. Various questions are suggested by this study. What land 

 area has been added to the continent by the river? What facts or fea- 

 tures observable on the map indicate delta area? What is the origin of 

 such lakes as Pontchartrain, Maurepas and Grand? How do the lakes 

 in the delta differ from those along the river above Baton Rouge? What 

 do the bays along the seaward border of the delta indicate as to the 

 manner of growth of the land area and of the origin of lakes in the 

 delta? Why does the river become straighter toward the mouth? What 

 is the cause of the abrupt bend just below New Orleans? Why does 

 the river flow so persistently to the southeast through the delta? 



It is generally stated that the delta extends from the mouth of Red 

 River southward because here the distrilnitary farthest upstream leaves 

 the river. This statement seems somewhat arbitrarily derived from the 

 earlier definition which describes a delta as the land included within the 

 divided mouths of a river, rather than the land formed by a river about 

 its mouth. A line extended from Baton Rouge to New Iberia connects 

 the south edges of the uplands on the opposite sides of the river and 

 seems a proper division between the filled valley above and the area of 

 added land or delta proper. South of this line, the great fan of the 

 delta projects, breaking the great curve of the north shore of the gulf. 

 Below this line the shape and size of the lakes change abruptly from 

 narrow, ox-bow lakes, formed by the river cutting across the necks of its 

 bends, to large, broad, irregular shaped lakes, evidently formed by irregu- 

 lar deposit, leaving areas of the gulf unfilled. Lake Pontchartrain, for ex- 

 ample, is a portion of the former gidf surface inclosed between the up- 

 lands to the north of it and the advancing delta on the south. Notice 

 how near the south shore of this lake the river fiows. Notice the stream 

 from within the limits of New Orleans extending along the strip of land 



