396 AGE OF THE MISSISSIPPI DELTA. 



voured to estimate the age of the Mississippi delta in the 

 following manner : " Dr. Kiddle," he says, " communicated 

 to me, at New Orleans, the result of a series of experiments 

 which he had made to ascertain the proportion of sediment 

 contained in the waters of the Mississippi. He concluded 

 that the mean annual amount of solid matter was to the water 

 as yAr i n weight, or about -g-^u 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 

 regularly with the increased height and velocity of the stream. 

 On the whole, comparing the flood season with that of clearest 

 water, his experiments, continued down to 1849, give an ave- 

 rage annual quantity 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. Forskey (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 assumed 528 feet, or the tenth of a mile, as the probable 

 thickness of the deposit of mud and sand in the delta ; found- 

 ing 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, one hundred fathoms, and partly on 

 some borings six hundred feet deep, in the delta near Lake 

 Pontchartrain, 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 annually brought down 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 only as equal to that of the delta, whereas 

 it is, in fact, larger." 



