118 REPORT—1846. 
hundreds of miles above the head of the delta, of the stumps of trees buried with 
their roots in their natural position, three tiers being occasionally seen one above the 
other, shows that the river in its wanderings has opened a channel through ancient 
morasses, where trees once grew, and where alluvial matter gradually accumulated. 
The old deserted bed also of the river, with its banks raised fifteen feet above the 
adjoining low ground, bears testimony to the frequent shifting of the place of the 
main stream, and the like inference may be drawn from the occurrence here and 
there of crescent-shaped lakes, each many miles in length, and half a mile or more 
in breadth, which have once constituted great curves or bends of the river, but are 
now often far distant from it. 
The Mississippi, by the constant undermining of its banks, checks the rise of large 
commercial towns on its borders, and causes a singular contrast between the wealth 
and splendour of 800 or more fine steamers, some of which may truly be called 
floating palaces, and the flat monotonous wilderness of uncleared land which ex- 
tends for hundreds of miles on both sides of the great navigable stream. 
Mr. Lyell visited, in March 1846, the region shaken for three months, in 1811-12, 
by the earthquake of New Madrid. One portion of it, situated in the States of Mis- 
souri and Arkansas, is now called ‘‘the sunk country.”’ It extends about seventy 
miles north and south, and thirty east and west, and is for the most part submerged. 
Many dead trees are still standing erect in the swamps; a far greater number lie 
prostrate. Even on the dry ground in the vicinity, all the forest trees which are of 
prior date to 1811 are leafless ; they are supposed to have been killed by the loosening 
of their roots by the repeated shocks of 1811-12. Numerous rents are also observa- 
ble in the ground where it opened in 1811, and many sink-holes or cavities, from ten 
to thirty yards wide and twenty feet or more in depth, now interrupt the general level 
of the plain, which were formed by the spouting out of large quantities of sand and 
mud during the earthquake. 
In attempting to compute the minimum of time required for the accumulation of 
the alluvial matter in the delta and valley of the Mississippi, Mr. Lyell referred to a 
series of experiments made by Dr. Riddell at New Orleans, showing that the mean 
annual proportion of sediment in the river was to the water 775 in weight, or about 
dso in volume. From the observations of the same gentleman and those of Dr. 
Carpenter, and of Mr. Forshey, an eminent engineer of Louisiana, the average width, 
depth and velocity of the Mississippi, and thence the mean annual discharge of water 
are deduced. 
In assuming 528 feet (or the tenth of a mile) as the probable thickness of the de- 
posit of mud and sand in the delta, Mr. Lyell founds his conjecture on the depth of 
the Gulf of Mexico, between the southern point of Florida and the Balize, which 
equals on an average 100 fathoms. The area of the delta being about 14,000 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 has 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. If some 
deduction be made from the time here stated, in consequence of the effect of drift- 
wood, which must have aided in filling up more rapidly the space above alluded to, 
a far more important allowance must be made on the other hand for the loss of mat- 
~ ter owing to the finer particles of mud not settling at the mouth of the river, but being 
swept out far to sea, and even conveyed into the Atlantic by the gulf-stream. Yet 
the whole period during which the Mississippi has transported its earthy burthen 
to the ocean, though perhaps far exceeding 100,000 years, must be insignificant in a 
geological point of view, since the bluffs or cliffs bounding the great valley (and there- 
fore older in date), and which are from 50 to 250 feet in perpendicular height, con- 
sist in great part of loam, containing land, fluviatile and lacustrine shells of species 
still inhabiting the same country, These fossil shells, occurring in a deposit re- 
sembling the loess of the Rhine, are associated with the bones of the mastodon, ele- 
phant, tapir, mylodon, and other megatheroid animals; also a species of horse, ox, 
and other mammalia, most of them of extinct species. The Joam rests at Vicksburg 
and other places on eocene or lower tertiary strata, which in their turn repose on 
cretaceous rocks. <A section from Vicksburg to Darier, through the States of Mis- 
