16 GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI. 
The following interesting and instructive section of the Corinth waterworks well was 
obtained from the waterworks company: 
Record of waterworks well, Corinth. 
Feet. 
Common soil 15 
Blue clay 20 
Sand 30 
Hard rock 1 
Sand, water bearing, supplying the shallow wells 35 
From 100 to 300 feet the strata are mostly hard "shale" clay, alternat- 
ing with beds of fine sand, which will furnish 225 gallons of water per 
minute with deep-well pumps; supply seems to be constant; water 
stands at top of casing , 200 
From 300 to 435 feet nothing but sandstone, limestone, and shale, with 
iron pyrite, but no water 135 
Selma chalk. 
Eutaw and Tuscaloosa 
Carboniferous, includ- 
ing Chester and St. 
Louis. 
Tullahoma flint, at 
base of which is 
found the fire clay 
which occurs at the 
base of the Tulla- 
homa along Tennes- 
see River. 
From 435 to 550 feet passed through gravel or "rock silica'' at the base 
of which was good fire clay 1 15 
551 
The well stopped in the fire-clay bed at the base of the Tullahoma. This section gives the 
most accurate and reliable data obtainable on the thicknesses of the different formations. 
There is a decided thinning of all the formations from south to north. The Selma, which 
Smith has estimated to be 930 to 1,200 feet thick in western Alabama, has thinned to 100 
feet at Corinth. The Tuscaloosa and Eutaw taken together have a thickness in the Corinth 
well of only 200 feet, while Smith has estimated the Tuscaloosa alone to be 900 to 1,000 
feet thick in western Alabama. 
SELMA CHALK. 
The subdivision of the Cretaceous immediately overlying the Eutaw formation is the Selma 
chalk. It was called " Rotten limestone " by Hilgard, but the name has since been discarded 
for that of the locality where it is typically exposed— Selma, Ala. — this name being first 
used by Dr. E. A. Smith of the Alabama Geological Survey. 
The Selma chalk is a mass of loosely semicemented lime carbonate of exceptional purity, 
and where typically exposed along the larger streams it has a white appearance and is called 
the "white chalk" bluffs. To the casual observer the entire formation has much the same 
appearance, but it may be separated into three natural divisions, based primarily on chem- 
ical analysis — (a) the sandy transition beds at the base, (b) the "blue rock," or more clayey 
unweathered portion, and (c) the "rotten limestone," or chalk, including the upper por- 
tion of the formation. 
(a) The lowest division contains a large amount of free sand which was washed into the 
Selma sea from the Eutaw and older laud surface to the east. This forms the transition 
beds from the extremely sandy portion of the Eutaw to the deep-sea deposits of lime car- 
bonate which characterize the Selma chalk. The amount of sand is greatest near the base 
and becomes less and less upward until it finally disappears entirely. 
(b) The middle portion contains a large amount of clay and when freshly dug is of a blu- 
ish color. It is found in the deep wells and is known and recognized by the drillers as "blue 
rock." The great amount of clay in the lime carbonate renders the rock impervious to 
water. The fine supply of artesian water stored in the Eutaw reservoir is held in place by 
the "blue rock" of the Selma. It is on account, therefore, of this impervious bed overlying 
the Eutaw that so many artesian wells are available over the Selma area. 
(c) The uppermost division contains a greater amount of lime carbonate and much less 
clay than the "blue rock" and likewise a smaller amount of free silica than the lowest divi- 
sion. Some of the analyses of this chalk show 98 per cent calcium carbonate. 
In places a hard crystalline limestone, somewhat silicified, forms a capping to some of the 
hills of the upper Selma. Hard flint rock and thin strata of sandstone are reported in the 
deep-well boring at Livingston, Ala. 
