48 GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI. 
the hills to the east. The pebbles found in wells throughout the delta are generally small 
and white, while those of the Lafayette are invariably iron stained and often quite large. 
The interpretation resulting from the present survey is that the vast so-called "Port Hud- 
son" deposits of the Yazoo delta are of much more recent date than the Lafayette, Port Hud- 
son, loess, and yellow loam, and are, to a greater or less degree, the reworked products of I 
these formations. 
LOESS. 
This highly interesting formation was first recognized in this country along the lower 
Mississippi by Sir Charles Lyell in 1846. In 1854 Wailes, in the report on the Agriculture 
and Geology of Mississippi, mentions the loess as occurring at various places along the Mis- 
sissippi. The following year G. C. Swallow, State geologist of Missouri, described the loess*] 
of Missouri River and gave it the name of Bluff formation. Ililgard used the same term for 
the loess in Mississippi in 1860. It has since received the attention of Chamberlin and 
Salisbury, McGee, Mabry, Binney, and Shimek. The latter, in Bulletin No. 4, vol. 5, of the 
State University of Iowa, presents a lengthy discussion of the loess at Natchez, Miss., ascrib- 
ing its origin to seolian agencies. His conclusions are based entirely on the fauna found in 
the loess. At Natchez and Vicksburg, t he two localities where he saw the loess, he found the 
material a highly calcareous, homogeneous mass, nonstratified and containing numerous 
land snails and other terrestrial forms. 
The loess is divisible into two distinct parts (a) the line, calcareous, gray to buff-colored] 
silt \ clays, containing numerous lime concretions and iron tubules, besides a great variety 
of fresh-water and land shells; | hi noncalcareous yellow to brown loam, void of shells. The 
latter has been described by Ililgard as the yellow loam. 
The hypsometrical relation of these two members varies in different places, as the follow- 
ing will show. Shimek a says: 
The loess [at Natche/.J is uniformly tin 1 uppermost deposit, forming the immediate subsoil on the ridge- 
on which Natchez is located. Underlying it in most of the exposures is the yellow or brown loam, 3 
which closely resembles loess, hut is not fossiliferous and is usually of a deeper red color, though some- 
times practically indistinguishable from it. 
In northern Mississippi Ililgard describes the yellow loam as overlying the loess. McGee 
places the yellow loam above the calcareous loess, but adds: 
The order of the first two members might lie reversed w ii h equal propriety in the southern portion of, 
the embayment; for the loess is hut a phase of the loam and is frequently underlain as well as overlain 
by the loamy deposits. 
Mabry refers to the yellow loam and loess as being not only homotaxial but synchronous 
as well. 
From observations made at various places in Mississippi, Tennessee, and Arkansas, the 
writer has reached the conclusion that all the above statements are correct. The yellow 
loam is only a modification of the typical loess. In other words, the loess changes in char- 
acter from a gray, calcareous, silt y material filled with shells to a reddish or yellow clay free 
from shells and calcareous matter. The positions of the two are interchangeable. At 
numerous places along Crowley Ridge, in Arkansas, the yellow clay both underlies and over- 
lies the typical calcareous loess, but there are no lines of division between the two; one grades 
insensibly into the other. 
In the vicinity of Bolton, Miss., and along Big Black River it is often impossible to draw 
any line where the loess ends and the yellow loam begins. The calcareous loess gradually 
blends upward into the more clayey loam. 
It is frequently the case that the yellow loam is entirely wanting, as at Helena, Ark., 
where the entire bluff is capped with the fossiliferous calcareous loess, which here shows 
faint lines of stratification. Still farther north, along Crowley Ridge, in Arkansas, the cal- 
careous loess is wanting and the bud' to yellow clay is at the top of the bluff overlying the 
Tertiary. 
a Bull. No. 4, vol. 5, State University of Iowa. 
