SECOND ANNUAL REPORT—STRATIGRAPHIC 'GEOLOGY. 105 
Section at Shell Bluff/(S: 4, T. 3, N., R. 21 PV). 
. , _ . . . ....... • 2 j 
S. Gravel covered slope, gravel elipsoidal, y 2 inch probably usual 
length, rarely 1 inch, mostly quartz, in rather coarse red Sands 30 feet. 
7. Gray, finer sand, blotched yellow, decidedly argillaceous, est...... 10 feet. 
C. Greenish shell marl, matrix arenaceous, fine fossiliferous (Shoal 
River marl member) ....... ..,-,.... 27 inches. 
5. Non-fossiliferous, coarser greenish sands, becoming argillaceous 
at base .... 3 feet. 
4. Green clay...... 6 inches. 
3. Coarser sands, gray, greenish, last 2 x / 2 feet, loose, purple and white 
sands .......... 6 feet. 
2. Unexposed ..... 15 feet. 
1. Non-fossiliferous green sands, oxidized yellowish on surface (Oak 
Grove sand member) . 10 feet. 
Total of section, about...... ... 80 feet. 
Lithologically this member consists of interbedded, greenish sands, 
clays and marls. The color is usually greenish, oxidizing yellow, 
occasionally whitish or purplish, and the material varies in texture 
from fine clay to sand. 
The Shoal River marl member of the Alum Bluff formation is 
about fifty feet thick. Some idea of its observed thickness may be 
gained from a study of the sections of the marl. This member of the 
Alum Bluff formation is very fossiliferous, and extensive collections 
were made by Dr. Vaughan, but they have not yet 'been studied in 
sufficient detail to permit the formulation of a comprehensive state¬ 
ment concerning the fauna. 
Dr. Vaughan 1 also examined the exposure at Senterfitt Creek. 
The fossiliferous marl forms a platform 20 to 30 feet wide along the base 
of the bluff, .sloping (at the present stage of the water) from 2 feet next the 
bluff to 1 foot along the river edge above the water. The surface in places is 
practically covered with shells freed from the matrix. The weathered marl is 
an ashy gray, but when fresh, dark bluish. 
After studying this exposure and collecting from it I revisited the exposure 
at Senterfitt Grist Mill, from which I collected in May, 1903. The latter lo¬ 
cality is by aneroid 30 feet above the fossil bed at the Oak Grove bridge; 
and is 2 miles northeast of that locality. The marl bed on Senterfitt Creek is, 
therefore, stratigraphically slightly above the Oak Grove horizon. 
The Senterfitt horizon seems very persistent, extending at least from the 
Yellow River to Argyle. 
Other localities mentioned by Vaughan 2 are : On the north side 
of the river, at the head of the first draw below Shell Bluff, about 
400 yards northwest'of the bluff, and 200 yards from the river; along 
the south side of Adam’s Mill Creek, near the top of a low bluff, and 
on Hulion Mill Creek, Sec. 7, T. 3, N., R. 21 W. 
1 Vaughan, T. Wayland. Unpublished notes. 
2 Vaughan, T. Wayland. Unpublished notes. 
