7C> GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI. 
(3) Tertiary limestones (Vicksburg limestone). 
The distribution of these formations is shown on the geologic map (PI. I), which is based 
on recent work by the United States Geological Survey in Mississippi. 
MISSISSIPPIAN (LOWER CARBONIFEROUS) LIMESTONES. 
In the extreme northeast corner of Mississippi, in the counties of Itawamba and Tisho- 
mingo, there is a small area of Devonian and Carboniferous rocks. These include shales, 
thin sandstones, and limestones. The limestones, which are mainly of Mississippian (Lower 
Carboniferous) age, are frequently low in magnesia, and are otherwise suitable for use as 
Portland cement material. At present, however, the most promising localities of these 
limestones have no adequate transportation facilities. This fact, together with the near- 
ness of the soft and easilj crushed Selma chalk, will probably serve to prevent the utilization 
of the Carboniferous limestones for some time. 
The following analysis of a limestone from Cypress Pond, Tishomingo County, is by 
Dr. E. W. Hilgard: 
Analysis of Mississippian limestone. 
Silica (Si0 2 ) 1 . 68 
Alumina ( A1 2 3 ) ■> 
lion oxide (Fej( >j) J 
Lime (CaO) 53. 49 
Magnesia (MgO) 82 
Carbon dioxide (C0 2 ) 42. 03 
Water 1. 34 
CRETACEOUS LIMESTONE (SELMA CHALK, OR " ROTTEN LIMESTONE"). 
The Selma formal ion <>f the Cretaceous is a thick series of chalks, chalky limestones, and 
more or less limy clays, which are well exposed in northeastern Mississippi. The area 
occupied by these limestones in Mississippi is shown in PI. I. 
Thickness. The Selma chalk attains its maximum thickness in central Alabama, reach 
ing a total of about 1,200 feet. To the west it decreases slightly in thickness, the well i t 
Livingston, Sumter County, Ala., giving a total of 930 feet, while the well at Starkville, 
Oktibbeha County, Miss., taken in connection with surrounding outcrops, indicates a thick- 
ness of at least 7(X) feet. As the belt turns northward toward Tennessee the formation 
decreases rapidly in thickness, while at the same time the limestone beds contained in it 
become fewer and thinner, until in Tennessee the Selma is a thin series of somewhat calca- 
reous clays, with only occasional beds of chalk. 
Stratigraphy. — Owing to the rapidity with which it disintegrates when exposed to atmos- 
pheric action, surface outcrops give comparatively little information in regard to the stratig- 
raphy of this formation. Fortunately, a very precise section of the Selma chalk, taken at 
a point where it is almost of maximum thickness, is in existence. This is embodied in the 
record of a well drilled at Livingston, Sumter County, Ala., and quoted by Dr. E. A. Smith 
in his Report on the Geology of the Coastal Plain of Alabama, pages 277-278. The well 
was located just south of the boundary between the Selma and Ripley formations, and 
reached a depth of 1,062 feet, so that it passed through the entire thickness of the Selma 
chalk and into the underlying Eutaw formation. 
The section of this well is given below. The upper 20 feet are, according to Smith, prob- 
ably in part Lafayette and in part Ripley. From a depth of 20 to 9.50 feet the well was in 
the Selma formation, while from 950 to 1,062 feet it was in the Eutaw. 
