182 Physics and Hydraulics of the Mississippi River. 
formule found in them, could not be relied upon for the solution 
of the questions upon which the plans of protection against in- 
undation from overflow depended. The system of measure- 
ments and investigations carried on at Carrolton, Louisiana; 
Vicksburg, Mississippi; and Columbus, Kentucky; while it was 
intended to render the solution of the problem of the protection 
of the alluvial region of the Mississippi against inundation inde- 
pendent of the laws and formule of the books, was at the same 
time designed, in connection with other parts of the Survey, to 
ord the means of determining, by experiments on a far more 
extended scale than any ever before attempted, the laws gov: 
erning the flow of water in natural channels, and of expressing 
them in formuls that could be safely and readily used in practl 
cal applications, The success that has attended this part of the 
work has even exceeded my expectations. Laws have been Te 
vealed that were before unknown; new formule have been pre 
pared, ssing far greater precision than the old; and improved 
methods of gauging streams have been devised. : 
But the imperfect state of the science of hydraulics as pie 
to rivers was not the only difficulty to be encountered in the ex 
ecution of the duty imposed upon the officer in charge of this 
work. The much agitated question of the best method of pro 
tection against inundation had been always discussed upon %* 
sumed data, and the truth of the very groundwork upon which 
these discussions rested had to be experimentally investi ted by 
this Survey. For instance, the Mississippi had always been tT 
rded as flowing through a channel excavated in the alluvial 
soil formed by the deposition of its own sedimentary matter. 
So important an assumption was inadmissible; and great pains 
were accordingly taken to collect specimens of the bed wherevé? 
soundings were made, and by every means to ascertain the depth 
of the alluvial soil from Cape Giradeau to the Gulf. This inves: 
tigation has resulted in proving that the bed of the MississipP! 
1s not formed in alluvial soil, but in a stiff, tenacious clay of an 
older geological formation than the alluvion, and that the sides 
of the channel do not consist of homogeneous material ; facts 
Further, it was held by the advocates of the exclusive ane 
that it was impracticable any + 
the country, except by opening new channels t0 
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