48 



MINERAL RESOURCES OF ALABAMA. 



per cent, of carbonate of lime, and 30 to 35 per cent, of silica, 

 alumina and iron. Its magnesia content is low, well within 

 the requirements for a Portland cement material. 



The limestone in some localities shows a considerable amount 

 of iron pyrites, however, which will cause the resulting cement 

 to carry a relatively high percentage of sulphates. 



The highly argillaceous character of the Selma Chalk has 

 the advantage that but little additional clay will be required to 

 make a perfect Portland cement mixture. 



In the table below, in addition to the analyses of rock con- 

 taining from 75 per cent, upwards of carbonate of lime, others 

 have been added of rock carrying less than 75 per cent, of this 

 ingredient, and which by proper mixture with the higher grades 

 of rock might make a cement mixture without the addition of 

 any clay. 



Table V. Composition of Selma Chalk. 



10. Bluff at Gainesville, Sumter Co 1 18. 42 1 10. 79 1 65.21) 1.57) .30 



