A. Tylor — Formation of Deltas. 



489 



clay, was found to be 63 feet thick. No. 48, 29 feet thick, very pure 

 clay. No. 42, 32 feet thick, leaden blue clay effervesced with acid. 

 No. 22 clay is described as identical with No. 19, and effervesced 

 with acid. No. 19, blue clay, with amber-coloured masses, each 

 containing a yellow pebble. The remaining 12 clay-beds only 

 amount to 205 feet in thickness, or an average of 17 feet each. 



As in the Delta of the Po, so in the Mississippi Delta, the lower 

 beds are the most sandy. Messrs. Humphreys and Abbot ^ give the 

 dimensions of the Delta as follows : — 



The area of the tract of alluvial land from Cape Girardeau to the 

 head of the assumed Delta, as given by previous writers, is too great. 

 By careful measurements upon the most authentic maps it is as 

 follows : — sauARE miles. 



The St. Francis bottom 6,900 



The Yazoo bottom 7,110 



The Tentas bottom . . , 4,440 



Small Swamps in the east bank, from Cairo to Baton Eouge 1.000 



19,450 



The area now drained by the Mississippi and its tributaries is esti- 

 mated at 2,455,350 square miles." 



From Humphreys and Abbot's report we learn that the Mississippi 

 water is never charged with matter in suspension up to the quantity 

 the water could hold. At high-water, both in 1857 and 1858, the 

 river held little more sediment per cubic foot than at dead low-water, 

 when the soundings of the Survey proved that the river made no 

 deposit in its channel. The caving in of the banks when the river is 

 falling temporarily affects the amount of sediment in the river. 





SLOPE OF THE MISSISSIPPI RIVEIl.^ 









Miles from 

 head 



High, -water 



Resultiag fall per mile in water surface. 





of passes. 



above gulf. 







Highwater. 







ft. inch. 





Miles. 



feet. 









(^ N S. W. pass 



> 17 



\ 0-165 









■^ I N. E. pass 



16 



0-175 









9 ( Passe 1' Outre 15 



(0.187 









O ; S. pass 



14 



; 0-200 



Head of Passes of "i 













Mississippi in Gulf > 







2 8 







.. 20 



0-115 



of Mexico ) 













Fort St. Philip ... 



20 



5 1 



... 



.. 84 



0-121 



Carrolton 



104 



15 3 



..* ••• « 



.. 72 



0-146 



Donaldsonville ... 



176 



25 8 



... . 



.. 52 



0-166 



Baton Rouge 



228 



33 9 



... ... 



.. 71 



0-220 



Eed River Landing 



299 



49 6 



... 



.. 62 



0-226 



Natchez 



361 



66 



... ... • 



.. 269 



0-309 



Vicksburg 



470 







.. 225 



0-320 



Games Landing ... 



630 



149 









Napoleon 



672 











Memphis 



855 



221 



,,, ... 



.. 204 



0-436 



Columbus 



1059 



310 



... ... 



.. 21 



0-571 



Cairo 



1080 



322 



... ... 



.. 173 



0-497 



St. Louis 



1253 



408 









1 Report on the Mississippi. U.S. War Department, 1864, p. 434. 



2 Op. cit.,p. 93. 3 Page 113, Humphreys and Abbot, 1864. 



