VICKSBURG FORMATION. 37 
The stratigraphic break between the Vicksburg and Jackson here seems to be the band of 
pure lignite which comes between the fossiliferous clay and the nonfossiliferous sand. Still 
farther down the river the sand at the base of the limestone shows at the water's edge, with a 
strong southward dip. 
This sandy nature of the upper Jackson may be traced throughout the length of the 
Jackson-Vicksburg contact. The most complete section showing the contact between the 
two formations was obtained on the east side of the ridge on the Siwel and Bradie road, in 
the NE. | sec. 22, T. 5 N., R. 1 W. The base of Vicksburg limestone here is 400 feet above 
tide. 
Section of Jackson and Vicksburg formations in sec. 22, T. 5 N '., R. 1 W. 
Feet. 
5. Thin strata of white and yellow sand 4 
4. Yellow sand with thin bands of iron sandstone, one-eighth inch in maximum thickness. The 
whole is interbedded with white, chocolate, and purple clays, the latter l\ inches thick 5 
3. Pure white sand 2\ 
2. Black lignitiferous clay 2 
1. Pure white siliceous sand containing mica .-. "> 
The remainder of the hill below is mostly covered with the wash from above, but where 
the strata are exposed they are highly stratified layers of sand gradually becoming more 
clayey near the base of the hill, and finally passing into a clay marl of the Jackson prairies at 
350 feet above tide. Whether this sand is the same as l he Red Bluff horizon, mentioned by 
IIilgard,a or not, it is impossible to say. Its stratigraphic position is the same, but no fossils 
have yet been found in the sandy strata. 
VICKSBURG FORMATION. 
The Vicksburg formation, first studied by Conrad, occupies an area lying just south of the 
Jackson formation and of much smaller extent. It consists of a semicrystalline limestone 
in beds varying from 1 foot to 3 feet in thickness, alternating with beds of sandy fossiliferous 
marl of about the same thickness. The beautiful, well-preserved fossils of the Vicksburg 
are mostly found in these beds of marl. This highly interesting formation marks the end of 
the marine conditions of the Tertiary in western Mississippi. Its outcrop occupies a narrow 
band just south of. the Jackson area and extends across the State from the typical outcrop at 
Vicksburg through Warren, Hinds, Rankin, Smith, Jasper, and Wayne counties into Ala- 
bama, where the Vicksburg and Jackson are inseparable on stratigraphic and paleontologic 
evidence, and are taken together and called the St. Stephens or White limestone. The 
Vicksburg outcrop is in most cases very narrow. Often the entire thickness is represented 
in one hillside. Where the country is more level the width of outcrop becomes greater, in 
places reaching 3 to 5 miles. 
There is a marked difference in the character of the various beds of limestone. Usually 
those near the surface are more or less affected by weathering, and have therefore become 
soft and often yellow. Below the zone of weathering the rock is often hard blue limestone 
suitable for a building stone. In some places the hard blue limestone occurs near the surface 
and forms small bluffs along the streams. 
There is no hard limestone of any consequence in the underlying Jackson and none in the 
overlying Grand Gulf, so that there is little possibility for mistaking the Vicksburg lime- 
stone. It is therefore a horizon easily recognizable in determining the dip of the Tertiary 
rocks. 
The thickness of the Vicksburg is usually overestimated. There are 6-5 to 75 feel of the 
alternating limestone and marl beds represented in the bluff at Vicksburg. At no other 
place h there found as great a thickness in one continuous section. Below the limestone are 
25 to 30 feet of lignitic clays and lignite. The full thickness of the formation is doubtless 
represented in the Vicksburg bluff. 
a Geology and -Agriculture of Mississippi, 1860, p. 135,, 
