GEOLOGY. 227 



has made another series of experiments, and his tables show that the 

 quantity of mud held in suspension increases regularly with the in- 

 creased height and velocity of the stream. On the whole, compar- 

 ing the flood season with that of clearest water, his experiments, 

 continued down to 1849, give an average annual quantity of solid 

 matter somewhat less than his first estimate, but not varying materi- 

 ally from it. From these and other observations on the average 

 width, depth, and velocity of the river, the mean annual discharge 

 of water and sediment was deduced. I then, (1846) assumed 528 

 feet, or the tenth of a mile, as the probable thickness of the deposit of 

 mud and sands in the delta ; founding my conjecture chiefly on the 

 depth of the Gulf of Mexico between the southern point of Florida 

 and the Balize, which equals, on an average, 100 fathoms, and part- 

 ly on some borings 600 feet deep, in the delta near Lake Pontchar- 

 train, 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 annually 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 years more 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, especially from some observations 

 made by Mr. Slidell during a government survey, which would lead 

 to the inference that the average number of cubic feet of water dis- 

 charged into the Gulf per second is considerably greater than was al- 

 lowed in the above estimate, I think it not improbable that the time 

 assigned is somewhat too long, as a larger quantity of sediment 

 would be brought down in a given time. But, on the other hand, it 

 must be remembered, that the delta is 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. Many circumstances, indeed, make me 

 doubt whether the larger portion of that impalpable mud, which con- 

 stitutes the bulk of the solid matter carried into the sea by the river, 

 is not lost altogether, so far as the progress of the delta is concerned. 

 So impalpable is the sediment, and so slowly does it sink, that a glass 

 of water taken from the Mississippi may remain motionless for three 

 weeks, and yet all the earthy matter will not have reached the bot- 

 tom. If particles so minute are carried by the current, setting for a 

 great portion of the year from west to east, across the mouth of the 

 river, into the Gulf Stream, and so into the Atlantic, they might ea- 

 sily travel to the banks of Newfoundland before sinking to the bot- 

 tom, and some of them, which left the head-waters of the Missouri in 

 the 49th degree of north latitude, may, after having gone southward 

 to the Gulf, and then northward to the Great Banks, have found no 

 resting-place before they had wandered for a distance as great as from 

 the pole to the equator, and returned to the very latitude from which 

 they set out. 



