CHAP. XXXIV.] AGE OF DELTA OF MISSISSIPPI. 189 



been brought down from the interior in a given time, and conse 

 quently a deduction would have to be made from the number of 

 centuries above stated on that account. But, on the other hand, 

 if it could be shown, by more accurate experiments and calcula 

 tions, that the quantity of water in the above computation was 

 greatly deficient, say even one-third less than the real quantity, I 

 do not imagine that any exaggeration has been made in the time 

 supposed to have elapsed since the rivers began to transport their 

 earthy ingredients to the alluvial plains of Louisiana. The delta 

 is, after all, a mere fragmentary portion of a larger body of mud, 

 the finer particles of which never settle down near the mouths 

 of the Mississippi, but are carried far out into the Gulf, and there 

 dispersed. 



The description which I have given of the great distance to 

 which the yellow and lighter streams of fresh water are seen 

 extending, from the various mouths, in the flood-season, into the 

 Gulf; and still more, the destruction of the banks and bars of 

 mud and sand caused by the tide scouring out the channels when 

 the river is low,^ and the strength of the marine current, run 

 ning ten miles an hour, and the stories of anchors and heavy 

 ballast cast up by the breakers high and dry on the shifting 

 shoals near the extremity of the delta, make me doubt whether 



delay. Such experiments as Mr. Sidell s, which give the velocity at various 

 depths and at different distances from the banks, are the more needed, 

 because it seems doubtful whether any correct mathematical formulae have 

 as yet been furnished for calculating the mean rate at which so deep a river 

 as the Mississippi flows, from observations made simply on its superficial 

 velocity. I placed all the data given me by Messrs. Riddell, Forshey, and 

 Carpenter, in the hands of my friend, Mr. George Rennie, F.R.S., to whom 

 we are indebted for many valuable papers on the application of the science 

 of hydraulics to rivers (see Report of British Association, vol. iii. p. 415, 

 1834), and, after examining them, he came to conclusions which did not 

 vary materially from those which I had previously announced. Mr. James 

 Nicol, Assistant Secretary of the Geological Society of London, before he 

 had seen Mr. Sidell s experiments, had expressed to me his belief that the 

 quantity of water carried to the Gulf by the Mississippi, must be greater 

 than I had assumed from Mr. Forshey s calculations, judging from the 

 amount usually assigned as the annual discharge of rivers having hydro- 

 graphical basins smaller than that of the Mississippi. 

 * See ante, p. 121. 



