TJic Loess of Natchc::, Miss. — Shiinek. 295 
such species as inhabit the warmer parts of our country today, 
and there is nothing in the molkiscan fauna of this loess which 
would suggest even the remotest possibility of a glacial cli- 
mate. 
It appears that the aeolian theory offers the best explana- 
tion of the origin of the loess not only of Natchez, but of all the 
Mississippi drainage. The writer's first paper in which a mod- 
ified form of the aeolian theory was presented,* was based al- 
most wholly on the study of fossils, and subsequent investiga- 
tions, geological, paleontological and botanical (for the loess 
presents an interesting problem to the plant ecologist, and the 
influence of plants on the formation of the deposit seems to be 
great), have only served to emphasize in the main the conclu- 
sions therein presented, though perhaps modifying them in 
some details. The chief purpose of the subsecjuent papers t 
was rather the demonstration of the impracticability and im- 
possibility of the generally accepted theories which postulated 
aquatic and glacial conditions. 
While it is not purposed here to enter upon a detailed dis- 
cussion of the positive evidence in favor of the aeolian theory, 
this being reserved for a more extended paper on that subject, 
certain considerations which have a direct bearing upon loess 
in general, and upon that of the southern Mississippi valley in 
particular, are here presented together with the writer's con- 
ception of the origin of the loess. 
To make the formation of such a deposit as- the loess pos- 
sible it is necessary to have : i ) A source of supply of ma- 
terial at hand; 2) an agency capable of transporting the ma- 
terial; and 3) a lodging place upon which it may be safely 
anchored. Where any of these conditions fail there can be no 
deposition of material, and no loess will be formed ; where 
these conditions are best developed there the deposit will be 
thickest. It has long ago been observed that the loess is best 
developed along our larger river-courses, and it is there that 
these conditions are all most likely to be presented. A more 
detailed reference to these conditions may be of interest : 
I. The source of supply. — It is quite generally conceded that 
the finely comminuted particles which make up the loess origin- 
*A Theory of the Looss.— Proc. la. Acad. Sci., vol. Ill, pp. 82-89.— 1896. 
tProc. la. Acad. Soi., vol. V, pp. 32-45, 1898; vol. VI. pp. 98-113, 1899; 
vol. VII, pp. 47-59. 1900. 
Journal of Geolosrv, vol. VII, Mch.. 1899. 
Bull. Lata. Xat. Hist. St. Univ. of Iowa, vol. V, pp. 195-212, May, 1901. 
