CHAPTER II. 



THE PORTLAND CEMENT MATERIALS OF CEN- 

 TRAL AND SOUTHERN ALABAMA. 



The raw materials suitable for the manufacture of Portland 

 cement, which occur in Central and Southern Alabama, are ar- 

 gillaceous limestones, purer limestones, and clays. 



The limestones valuable as cement materials occur mainly 

 at two horizons, viz., in the Selma chalk or Rotten limestone 

 of the Cretaceous, and in the St. Stephens formation of the 

 Tertiary. The clays available are residual clays from the de- 

 composition of the two limestone formations above mentioned, 

 the stratified clays of the Grand Gulf formation, and alluvial 

 clays occurring in the river and creek bottoms. It is further 

 possible that later investigation may show that some of the 

 other stratified clays of the Tertiary formations are suitable, 

 and this is especially likely to be the case with the clays of the 

 lowermost Cretaceous or Tuscaloosa formation. 



THE SELMA CHALK OR ROTTEN LIMESTONE. 



Geological horizon. The Cretaceous system in Alabama is 

 susceptible of classification into four divisions, which are, in 

 ascending order, 



1, the Tuscaloosa, a formation of fresh-water origin, 

 made up in the main of sands and clays in many altera- 

 tions. In places the clays occur in deposits of sufficient 

 size and of such a degree of purity as to make them of 

 commercial value. 



2, the Eutaw, which is of marine origin and composed 

 of sands and clays more or less calcareous, but nowhere 

 showing beds of limestone properly so called. 



3, the Selma chalk, which is of marine origin, and is 

 composed, in part at least, of the microscopic shells of 

 Foraminifera. 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 



