49 



between Lake Poutt-liartraiii and Lake Borgne. This stream is evidently 

 a former distributary of the main stream. Tlie bays along the edge of 

 the delta of which I'.arataria. Timl)alier j-nd Ti rre Bonne are examples, 

 show how the advancing delta arms extend around areas of gulf and 

 hem them in. Notice particularly Bay Marchand. at the mouth of Bayou 

 la Fourrhe. and the separation of Timbalier and Terre Bonne bays by the 

 long narrow delta of Bayou Terre Bonne. 



This inclosing process is aided by the formation of barrier beaches 

 from point to point by wave action. True delta area is further indicated 

 by the straighter course of the river below Baton Rouge. The river is 

 very meandering through the whole length of the alluvial valley on 

 account of the gentle slope of the river bed. but below Baton Rouge it 

 becomes increasingly straight, although n\ the distance of two hundred 

 forty miles the fall is but five feet, or one-fourth inch per mile. As 

 streams always acquire the meandering haltit on gentle slopes, this ap- 

 parent contradiction of the law of stream flow furnislu's an interesting 

 problem. I piopose this explanation: The river flowing into the gulf 

 produces a current some distance out from the shore along the sides of 

 which the sediment is deposited more rapidly than in the swifter central 

 line of flow. Finally the narrow mud banks appear above the surface 

 along the course laid (lut l)y the current in the still waters of the gulf. 

 The tendiMii-y to meander shown at the head of the delta indicates the 

 inclination of the stream to conform to law. The stream is forming 

 meanders. Below New Orleans an abrupt Itend appears as an apparent 

 refutation of the explanation of the straight lower course. This bend 

 represen;s an accident in the direct forward movement of the delta. Ob- 

 serve the streams beginning near the eastern curve of this bend and the 

 tract of land extending east and pai'tially inclosing Lake Borgne and 

 Mississippi Sound on the south. These streams and this strip of land 

 indicate a former course of the river. A crevass across the narrow south 

 bank caused the abandonment of the part below and the abrupt turn of 

 the river. A crevass called "The Jump," twenty miles above the mouth 

 of the river, indicates how a repetition of the above accident may occur. 

 A sulimarine fan is ai»proaching the surface outside of this gap. The 

 southeast trend of the river through the delta and of the main area of 

 the delta itself may be due to the eastward movement of the Gulf 

 Stream off shore which detlected the incoming river current to the east. 



4— A. or SciE.NPK, '04. 



