V APPENDIX, 



In addition to the matter transported in suspension by the 

 river's current, tliere is borne forward by the mechanical force of 

 the waters a vast vokirae of material of coarser and heavier kind, 

 which is rolled and pushed along the bottom of the channel, be- 

 lieved by the writer to exceed in volume the suspended matter 

 by five (possibly twenty) fold. Its quantity is immeasurable, 

 but proved to be vast. 



As moving water in any river has many oblique currents, due 

 to irregularity of channel surfaces, much of the transported mine- 

 ral matter is kept in suspension, in spite of its specific gravity. 

 In consequence, the forward-moving matter may be, and often 

 is, lifted and dropped again and again, thousands of times, ia 

 its progress. Whenever any volume of water drifts into an 

 eddy, or finds a slower movement, portions of its sediment are 

 dropped, only to be lifted again when impinged on by an oblique 

 and upward current. Along a bottom of ascending plane, even 

 heavy materials are rolled or pushed upward to greater eleva- 

 tions, even to the river's surface, and thus frequently are thrown 

 out upon the highest banks, where obstructed currents can no 

 longer drift them forward ; and they thus form permanent addi- 

 tions to the land. 



It is thus that the immediate front banks of the river are 

 highest. The escaping waters, retarded by obstructions, leave 

 their heaviest load of sand near the banks, and bear forward the 

 lighter materials into the lower grounds, back from the front 

 banks. And thus is realized and explained the familiar fact that 

 the front surface-lands are of heaviest and often coarse sandy 

 material, while the remoter surfaces are of more tenacious and 

 clayey composition * 



The river and its auxiliary bayous have thus occupied, at 

 various periods, nearly all the areas of the delta, building up, 

 carving away, and replacing the beds of alluvion, varying in 

 character from coarse sand to the finest blue clay, all over the 

 basin. 



It'is obvious, in this process of changing its channel and re- 

 newing its walls, that the river must have many lower and 

 higher portions in its banks, and that in considerable floods the 

 water must be pouring out at many places, and finding its way 

 down the delta through the laterals, and often through the forests, 

 that cover the lower, but mainly emerged, portions of the basin. 

 And hence the necessity, when man claimed the occupancy of the 

 delta, of levees. 



Levees. — When the French discoverers pitched their pal- 



* It must not be inferred, hence, that these facts appear at all depths in 

 the alluvial basin ; for in the shifting of channels, sand-banks are of. en 

 covered by clayey material, and the converse. The river's caving banks 

 illustrate this in multiplied instances. No rule applies to sections of the 

 alluvion ; they diifer at every hundred or thousand feet. 



(14) 



