72 CEMENT MATERIALS AND INDUSTRY. [bull. 243. 
SELMA CHALK OR " EOT TEN LIMESTONE." 
GEOLOGIC HORIZON. 
c 
The Cretaceous system in Alabama is susceptible of classification 
into four divisions. These are, in ascending order, the Tuscaloosa, 
the Eutaw, the Selma chalk, and the Ripley. 
The Tuscaloosa is of fresh -water origin and is made up in the main 
of sands and clays in many alternations. In places the clays occur inj 
deposits of sufficient size and of such a degree of purity as to make 
them of commercial value. The Eutaw is of marine origin and is com- 
posed of more or less calcareous sands and clays, but nowhere shows 
beds of limestone property so called. The Selma chalk is of marine] 
origin and is composed, in part at least, of the microscopic shells of 
Eoraminifera. This formation, throughout the western part of the 
belt covered by it in Alabama, is about 1,000 feet in thickness, and is 
made up of beds of chalky and more or less argillaceous limestone. In 
a general way it may be said that the lower and upper thirds of the] 
formation contain 25 per cent or more of clayey matters mixed withji 
the calcareous material, while the middle third will hold less than 25 
per cent of these clayey impurities. The Ripley, like the preceding,], 
is a marine formation, in which, generally, the calcareous constituents}} 
predominate, but in places it contains sandy and clayey beds. 
From this summary it will be seen that the Selma chalk is the only 
one of the Cretaceous formations in Alabama which offers limestone in|i 
such quantity and of such composition as to be fit for Portland cement: 
material. 
LITHOLOGIC DESCRIPTION. 
As has been stated above, the Selma chalk is a calcareous formation 
throughout its entire thickness of about 1,000 feet. The rock, how- 
ever, varies in composition between somewhat wide limits; for this 
reason three divisions may readily be distinguished. The rock of the 
upper division is highly argillaceous, holding 25 per cent or more oi 
clayey matters; portions of it are composed of calcareous clays on 
marls rather than limestone, and in these beds are found great num-1 
bers of fossils, mainly oysters. Along Tombigbee River these beds 
make the bluffs from Paces Landing down nearly to Moscow, and orJ 
the Alabama they form the banks of the river from Elm Bluff dowra 
to Old Lexington Landing. The strata exhibited in these bluffs con 
sist of dark-colored, fossiliferous, calcareous clays alternating with 
lighter-colored and somewhat more indurated ledges of purer, less - 
argillaceous rock. At Elm Bluff, which is about 125 feet high, the 
upper half of the bluff is of this character. The lower half of the 
bluff is composed of rock more uniform in composition and freer from 
clay, and is the top of the middle part of the Selma formation, which is 
made up of limestone of more uniform character, containing gener-j 
ally less than 25 per cent of clayey material. 
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