TERTIARY ROCKS. 23 
Main street and in the gullies east of the street. Here the same relations exist as at the 
hill one-half mile east of the bridge mentioned above. 
The thin ledge of hard green calcareous sandstone on top of the yellow sand has more 
the appearance of a limestone. Its thickness is 24 to 26 inches. 
Two and a half miles east of Ripley, on the Ripley and Boonville road, the Clayton lime- 
stone occurs in a deep ravine, as shown in the following section. Some distance down the 
creek the "Owl Creek" marl occurs at a lower elevation. 
Section of Clayton limestone 2\ miles east of Ripley. 
Ft. In. 
6. Greenish-yellow sand, similar to that at Ripley 10 
5. Upper stratum of hard limestone with large Turritella fossils 1 3 
4. Yellow to gray marl containing numerous large Turritella 20 
3. Hard flinty limestone with no Turritella, but containing a small branching coral 26 
2. Indurated marl containing large Turritella 12 
1. Lowest stratum visible is the Turritella rock, which here is made up almost entirely of these 
fossils 42 
The same Turritella limestone that is found 2\ miles east of Ripley shows in many ravines 
east of Muddy Creek in the vicinity of Chalybeate. At a few places, as at Chalybeate 
Spring, the underlying Ripley marl is exposed. The limestone occurs as ledges from 3 to 6 
feet thick. On Mr. Bobo's place, 1^ miles north of Chalybeate, the limestone is overlain by 
about 30 feet of yellow sandy marl containing numerous fragile fossils. At the top of the 
yellow sandy marl is a thin band of green sandstone containing mica. The order of strata 
here is the same as it is at Ripley, and the materials are but little different in general litho- 
logic character. 
The most complete list of fossils from the Midway group in Mississippi is given by G.'D. 
Harris in American Paleontology, No. 4, pages 22-25. 
PORTERS CREEK CLAY. 
This formation was described by Doctor Hilgard in his Geology and Agriculture of Missis- 
sippi under the term Flatwoods clays. It is known in Alabama as the Black Bluff or Suc- 
arnochee series, and was described by Safford of Tennessee as Porters Creek. The term 
Porters Creek as used by Safford has priority of date and has therefore been adopted by 
the United States Geological Survey. 
The Porters Creek clay is traceable across western Kentucky, Tennessee, and Mississippi, 
and as far east as Alabama River in Alabama. 
The area in Mississippi is a narrow belt from 2 to 15 miles wide, extending across north- 
eastern Kemper, southwestern and western Noxubee, northeastern Winston, western 
Oktibbeha, Clay, and Chickasaw, west-central Pontotoc and Union, and western Tippah 
counties. The typical "Flatwoods" is characterized throughout the State by low, flat land 
resembling the broad bottom of a large river. In many places the country is still uncleared 
and is everywhere known as the "Flatwoods country." 
The material of the Porters Creek formation in the lower part is principally a dark -gray 
joint clay, overlain by a coarse-grained micaceous sandstone containing large fossils. 
Occasionally it weathers almost white; and in places it is a black slaty clay, bearing fossils. a 
In places the clay contains bodies of micaceous sandstone that seem to have been segregated 
into horizontal sheets and vertical masses, many of which have the appearance of small 
dikes. It is quite possible that small fissures have been made in the clay by earthquakes 
and subsequently filled with micaceous sand. 
Hilgard b m describing the physical properties of the Porters Creek or "Flatwoods" clays, 
says: 
This Flatwoods clay does not "readily dissolve" or form a plastic paste with water; but whenever by 
dint of repeated kneading (such as the wheels of vehicles will perform) it has been made to form a paste, its 
tenacity is such as to be scarcely exceeded by the most approved "prairie mud." Nor can the black 
« Coastal Plain of Alabama, p. 186. & Geology and Agriculture of Mississippi, 1860, p. 275. 
