118 Scientific Intelligence. 
4. On the Mississippi Delta; by C..LyE.t, (in a letter to the edi- 
tors.)*—In a previous letter, | mentioned.to you that the report of my 
discourse on the delta of the Mississippi; which appeared in the Ath- 
eneum Journal, Sept. 26th, 1846, although corrected by me, was no 
ered to the British Association at Southampton. It failed to embrace 
even the heads of many of the arguments and data, which I adduced, 
and as | find that it has not been so understood by all, I am desirous of 
supplying one or two of the most obvious omissions. In my conjectural 
estimate of the probable thickness of the alluvial deposit, | alluded not 
only to the ascertained depth of the Gulf of Mexico, between the 
southern point of Florida and the Balize, but also to some borings, 
feet deep, made to the northward of New Orleans, near Lake Pont- 
chartrain, in which the engineers say they failed to reach the bottom of 
the Mississippi mud. In regard to the depth of the alluvium, above the 
head of the delta, [ remarked in my lecture, that the river, in its wan- 
derings over the alluvial plain, had every where cut out deep channels 
from 60 to 250 feet deep, and that the excavations thus made had been 
filled again, with the exception of certain bayous and crescent-shaped 
lakes, which remain as monuments of some of the former positions oc- 
part of the large basin, or receptacle of sediment, even if we sup- 
pose it to have been originally very shallow, which I know no reason 
for presuming. 
I have lately received a letter from Dr. Carpenter of New Orleans, 
from which I am happy to Jearn that my friend, Dr. Riddell, is repeat- 
ing his experiments on the quantity of earthy matter held in suspension 
in the waters of the Mississippi. It appears from the observations 
already made, that after duly allowing for the greater clearness of the 
nably the od, 
which the Mississippi has taken to accumulate its allu’ 
The new result will still differ remarkably from that obtained by Mr. 
Horner, in his measurement of the quantity of earthy matter in the 
Rhine at Bonn, which in volume was +¢4y¢ 37 but it contrasts still more 
strikingly in an opposite way, from the conclusions of Mr. Everest, in 
regard to the Ganges, where the proportion of solid matter, duri 
even months of the year, (a period in which nearly the total annual 
discharge of water takes place,) was found to be x3, in weight, dr git 
in bulk.t But in this case, we have to bear in mind not only the great 
height of the Himalaya Mountains, but also how much nearer the 
- 5 London, Nov. 6, 1846, and intended as an addition to the article on p- 34. 
+ Edin. New Phil. Jour., Jan., 1835. iis eee 
- $ Jour. of Asiatic Soc., No. 6, p. 238, June, 1832. See also Mr. Prinsep, Glean- 
ings in Science, Vol. iii, p. 185. Also Principles of Geology, Book UM. 
