II. 



' ON THE ALLUVIAL BASIX OF THE MISSISSIPPI 

 RIVER STYLED THE DELTA. 



By prof. C. G. FORSHEY. 



(Read 1874, March 28.) 



The Mississippi River has a hydrographic basin embracing 

 1,244,000 square miles * The rainfall upon this area, and its 

 abrasions in travel towards the Gulf, have thrown upon the basin 

 belov^r Cape Girardeau, an alluvial bed, extending thence south- 

 ward to the sea, whose area is computed by Prof. Forshey at 

 38,*706 square miles, about -^^-^ of the entire hydrographic basin. 



The river runs through this basin, its present channel skirting 

 the bluffs, or diluvial uplands, on the east, from the head of the 

 Delta, as above, to the south boundary of Tennessee, lat. 35°, a 

 few miles below Memphis; thence to the mouth of the Yazoo 

 River, above and near Vicksburg, lat. 32° 22', the channel 

 winds midway through the alluvion, and again impinges the 

 bluffs with its east bank ; thence it keeps close to the bluffs to 

 Baton Rouge, Louisiana, lat. 30° 28'; and thence to its mouth, 

 at lat. 29^, winds through the alluvial bed 245 miles, projecting 

 more than 100 miles into the Gulf of Me.xico. 



Delta Boundary. — The alluvion is bounded on the left or 

 eastern limit by bluffs of some elevation even where the river does 

 not impinge upon them; whereas, the western limit of its basin is 

 very obscure in most of its length, and, though easily recognized 

 by the eye of the geologist, the uplands rise so gently above the 

 alluvial level as to present no definite boundary to the floods 

 that annually cover large areas of the alluvion. 



On the west or right boundary the limit may be run from the 

 river at three miles below Cape Girardeau, lat. 37° 20', south- 

 westwardly through the AVhite Water Creek and the Castor 

 Lakes to the St. Francis River; thence across the bottom of 

 this river to Black River, and with the, right of its alluvion down 

 to White River, and with the western limit of its alluvial bottom 

 to the confluence of this and the Arkansas River. Thence the 

 limit runs up the Arkansas to near and below Pine Bluffs, across to 

 the Bartholomew, with its right bank to the Washita, and down 

 west of the alluvion of this river to Harrisonburg, lat. 34° 48'; 

 thence the alluvion basin is bounded by bluffs to the north shore 

 of Lake Ocatahoula and its outlet, the Saline, to Red River ; 



* In an article published in the Concordia Intplligencer, .Jan. 20, 1840, 

 Prof. Forshi^y computes tiie area of tlie basin at 1.300,000 mil^s The 

 Delta survey of Humphreys and Abbott gives 1,244,000 provisiouallj 

 adopted till uiore accurately determined. 



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