Note 367 — Chapter XVIII

The calculations here given were communicated to the British Association, in a lecture which I delivered at Southampton in September, 1846. (See Athenæum Journal, Sept. 26, 1846, and Report of British Association, 1846, p. 117.) Dr. Riddell has since repeated his experiments on the quantity of sediment in the river at New Orleans without any material variation in the results.

Mr. Forshey, in a memoir on the Physics of the Mississippi, published in 1850, adopts Dr. Riddell's estimate for the quantity of mud, but takes 447,199 cubic feet per second as the average discharge of water for the year at Carrolton, nine miles above New Orleans, a result deduced from thirty years of observations. This being one-tenth more than I had assumed, would add a tenth to the sediment, and would diminish by one-eleventh the number of years required to accomplish the task above alluded to. "The cubic contents of sedimentary matter," says Forshey, "are equal to 4,083,333,333, and this sediment would annually cover twelve miles square one foot deep."