APPENDIX. IV 



particular it has no parallel known to civilized man." These 

 bayous and rivers have their channels mainly parallel to the 

 river's course, and they serve as drains to the rain-waters fall- 

 ing upon the delta ; and before levee history, and partially now, 

 they serve to bear off the waters that overflow the lower portions 

 of the banks of the Mississippi itself. 



The depths of the greatest undulations below the river's high- 

 water level are about thirty-seven feet, though such depressions 

 are very rare. Ten, twelve, and fifteen feet are much more com- 

 mon ; but all the depressions are greater at the greater distances 

 from the present channel.* The average depth reduced from all 

 the sections leveled, is about 12 feet. The delta sea, if raised 

 to the level of the river, at like latitudes, would have a mean 

 depth of 12 feet. In all great floods, then, the entire delta is 

 menaced by the river's flowing reservoir of 12 feet average depth 

 of water. Thus much does the great river lack of having filled 

 and replaced with deposits what has been carried away by its 

 erosions. 



Peculiarities op the Physics of the River. — The mode by 

 which the river Mississippi produces the formation of tlie alluvial 

 delta, is not in general terms different from that of any river or 

 rivulet, whether great or small. 



In some particulars the mode is peculiar ; and as these peculiari- 

 ties have been determined by the most elaborate investigation yet 

 given to any great river, the writer upon these phenomena can 

 speak with confidence, and may once for all give credit to the great 

 work of Humphreys and Abbott on the " Physics and Hydraulics 

 of the Mississippi River." 



The greatest of these peculiarities is found in the perpetual tur- 

 bidness of the waters. Three rivers from the west, the Missouri, 

 the Arkansas, and the Red River, contribute turbid waters in 

 both flood and low-water seasons. The Missouri, how^ever, 

 yields the greater portion of the transported matter, and gives 

 the muddy hue to the waters; the other two rivers yield ferru- 

 ginous matter, tinged with red, that modifies the color of the 

 river below them, especially in flood seasons of these rivers. 



The Mississippi bears in suspension an allurainous clayey 

 matter, of extremely fine comminution, that amounts in quantity 

 to about one part by weight in 1800, and by measurement one 

 volume in nearly 3000, as shown by many thousands of careful 

 tests, carried through two entire years, and derived from all 

 portions of the river's flowing volume. f 



* The river bank of the Washita, at 75 miles wpst from Vicksbiirg, is 

 12 ft-et below the Missi.ssippi's bank ; and on this line of leirels, at only 12 

 miles east of the Washita, the land is 38 feet below the Mississippi level ; 

 the greatest depression found in the 15 lines of level run across the delta. 



t The writer hereof performed these measuretannts, as well as others, 

 as the Hydrometrio Engineer's Assistant of the Delta Survey. 



(13) 



