CHAP. XXXIV.] OF DELTA OF MISSISSIPPI. 249 



Dr. Riddell communicated to me, at New Orleans, 

 the result of a series of experiments which he had 

 made, to ascertain the proportion of sediment con 

 tained in the waters of the Mississippi. He con 

 cluded that the mean annual amount of solid matter 

 was to the water as T ^Vj m weight, or about 3 oij o 

 in volume.* Since that period, he has made another 

 series of experiments, and his tables show that the 

 quantity of mud held in suspension, increases regu 

 larly with the increased height and velocity of the 

 stream. On the whole, comparing the flood season 

 with that of clearest water, his experiments, con 

 tinued down to 1849, give an average annual quan 

 tity of solid matter somewhat less than his first 

 estimate, but not varying materially from it. From 

 these observations, and those of Dr. Carpenter and 

 Mr. Forshey (an eminent engineer, to whom I have 

 before alluded), on the average width, depth, and 

 velocity of the Mississippi, the mean annual discharge 

 of water and sediment were deduced. I then as 

 sumed 528 feet, or the tenth of a mile, as the pro 

 bable thickness of the deposit of mud and sand 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 partly on some borings, 

 600 feet deep, in the delta near Lake Pontchar- 



* The calculations here given, were communicated to the 

 British Association in a Lecture which I delivered at South 

 ampton, in September, 1846. See &quot;Athenaeum Journal,&quot; 

 Sept. 26. 1846, and &quot;Report of British Association,&quot; 1846, p. 1 17. 



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