250 COMPUTATION OF AGE [CHAP. XXXIV. 



train, north of New Orleans, in which the bottom of 

 the alluvial matter is said not to have been reached. 

 The area of the delta being about 13,600 square 

 statute miles, and the quantity of solid matter an 

 nually brought down by the river 3,702,758,400 

 cubic feet, it must have taken 67,000 years for the 

 formation of the whole ; and if the alluvial matter 

 of the plain above be 264 feet deep, or half that of 

 the delta, it must have required 33,500 more years 

 for its accumulation, even if its area be estimated 

 as only equal to that of the delta, whereas it is in 

 fact larger. 



From information since received, I think it not 

 improbable that the quantity of water may have 

 been underrated in this estimate* ; and, if so, a larger 



* I allude chiefly to the observations and experiments, on 

 the velocity of the Mississippi at various depths, made by 

 Mr. W. II. Sidell, during a Government survey, communicated 

 to me through the kindness of Mr. Ruggles, of New York, 

 which, if correct, would lead to the inference that the average 

 number of cubic feet of water discharged into the Gulf per 

 second, is considerably greater than Mr. Forshey and Dr. Car 

 penter deduced from their observations on the velocity of the 

 stream at different depths. If, as I understand, there exist 

 documents in the hydrographer s office at Washington, which 

 would afford more ample data for such calculations, the Govern 

 ment would confer a boon on the scientific world by publish 

 ing them without delay. Such experiments as Mr. Sidell s, 

 which give the velocity at various depths and at different dis 

 tances from the banks, are the more needed, because it seems 

 doubtful whether any correct mathematical formulas 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 



