CEMENT RESOURCES: SELMA CHALK. 



47 



nish material suitable for admixture with the limestone, the 

 underlying clays being apparently slightly better in composition 

 than those of the shales of the Coal Measures above the lime- 

 stone. The Cretaceous clays appear to be entirely suitable. 



Table IV. Composition of Clays and Shales near Lower Carbonifer- 

 ous Limestone. 



*Trace. 



The shales and clay in Table II above are also available for 

 the Bangor limestone. 



3. The Selma Chalk (Cretaceous}, of Middle Alabama. 



Areal Distribution. The Selma Chalk or "Rotten Lime- 

 stone" outcrops as an east and west trending belt, Eutaw, Selma 

 and Montgomery, being near its northern, and Livingston, 

 Linden, Union Springs, near its southern border. In its widest 

 portion, towards the western part of the state, this belt is about 

 25 miles from north to south, but it thins to the eastward, dis- 

 appearing entirely some 15 miles west of Columbus, Ga. The 

 belt is intersected by the Alabama, Tuscaloosa, and Tombigbee 

 rivers, and a characteristic bluff of this reck is shown in Plate 

 V, a view of the left bank of the Tombigbee River at Demo- 

 polis. 



Chemical Composition. The Selma Chalk is about 1,000 

 feet in thickness, and is in general terms a very argillaceous, 

 chalky limestone, varying considerablv in the proportion of 

 clayey matters in its different parts. In the upper and lower 

 thirds of the formation, the proportion of clay is high and car- 

 bonate of lime will not usually exceed 60 or 65 per cent. 



The rock of the middle third of the formation, which is the 

 part best suited for cement making, will average about 70 to 85 



