kel] Mississippi. 207 
The following analysis of a limestone from Cypress Pond, Tisho- 
lingo County, is hy Dr. E. W. Hilgard: 
Analysis of Mississippian limestone. 
lica (Si0 2 ) 1.68 
lumina ( A1 2 3 ) 1 rn 
on oxide (Fe 2 3 ) 
me (CaO) . 53.49 
agnesia (MgO) 82 
rbon dioxide (C0 2 ) 42. 03 
ater . „ 1. 34 
CRETACEOUS LIMESTONE (SELMA CHALK OR " ROTTEN LIMESTONE"). 
The Selma formation of the Cretaceous is a thick series of chalks, 
alky limestones, and more or less limy clays, which are well exposed 
northwestern Mississippi. The area occupied b\ T these limestones 
shown on PI. II, and a very detailed description of the Alabama 
eas of Selma chalk is given in Doctor Smith's discussion of the 
ment resources of Alabama in this bulletin (pp. 72-77). 
Thickness. — The Selma chalk attains its maximum thickness in cen- 
I Alabama, reaching a total of about 1,200 feet. Westward it 
creases slightly in thickness, the well at Livingston, Sumter County, 
a. , giving a total of 930 feet, while the well at Starkville, Oktibbeha 
Hint} 7 , Miss., taken in connection with surrounding outcrops, indi- 
tes a thickness of at least 700 feet. As the belt turns northward 
ward Tennessee the Selma formation decreases rapidty in thickness, 
rile at the same time the limestone beds contained in the formation 
come fewer and thinner, until in Tennessee the Selma is a thin 
ries of somewhat calcareous clays, with only occasional beds of chalk. 
Stratigraphy. — Owing to the rapidity with which it disintegrates 
len exposed to atmospheric action, surface outcrops give compara- 
bly little information in regard to the stratigraphy of the Selma 
rmation. Fortunately a very precise section of the Selma chalk, 
sen at a point where it is almost of maximum thickness, is in exist- 
ce. This is embodied in the record of a well drilled at Livingston, 
fmter County, Ala., and quoted by Dr. E. A. Smith in his Report 
the Geology of the Coastal Plain of Alabama, pages 277-278. The 
II was located just south of the boundary between the Selma and 
pley formations, and reached a depth of 1,062 feet, so that it passed 
ough the entire thickness of the Selma chalk and into the under- 
ng Eutaw formation. 
The section of this well is given below. The upper 20 feet are, 
cording to Smith, probably in part Lafayette and in part Ripley, 
om a depth of 20 to 950 feet the well was in the Selma formation, 
iile from 950 to 1,062 feet it was in the Eutaw. 
