CEMENT RESOURCES: TRENTON LIMESTONE. 43 



Portland cement plants near the coal mines would give to this 

 industry in Alabama- the same advantages which the proximity 

 of the iron ore, the coal, and the stone has given to the iron in- 

 dustry, and which has placed our state beyond competition. 



As a Portland cement mixture, ready for burning, consists 

 approximately of 75 per cent, lime carbonate and 25 per cent, of 

 clayey matter, the material furnishing the lime carbonate is 

 necessarily of more economic importance than that from which 

 the silica and alumina are derived. In consequence, a Portland 

 cement plant is usually located in the immediate vicinity of a 

 suitable limestone, while the clay or shale required to complete 

 the mixture may be brought some distance. In the present 

 statement, therefore, the Alabama localities where cement in- 

 dustries may be developed will be discussed under four head- 

 ings, according to the limestone available in each locality. 



Disregarding limestone formations whose chemical composi- 

 tion renders them unsuitable for use in the manufacture of 

 Portland cement, as well as those whose outcrops are small or 

 badly located with regard to transportation routes, the lime- 

 stones oi four formations may be considered as particularly well 

 adapted for use in cement manufacture. These are : 



(1) Trenton limestone ( Silurian V of Northern Alabama. 



(2) Bangor limestone, (Lower Carboniferous), of Northern 

 Alabama. 



(3) Selma chalk (Cretaceous), of Middle Alabama. 



(4) St. Stephens limestone, (Tertiary), of Southern Ala- 

 bama. 



i. Trenton Limestone. 



Arecd Distribution. The Trenton limestone occurs in all the 

 northeast and southwest trending valleys of Northern Ala- 

 bama, outcropping usually in a narrow belt near the base of 

 the Red Mountain ore ridges, though sometimes occurring high 

 up on the flanks of these mountains, and in some localities 

 underlying considerable areas of lowlands in the valleys, as at 

 Pelham, Siluria, Longview, Calera, Shelby, Rock Springs, etc. 



Chemical Composition. As this rock is extensively quarried 

 for lime burning and for furnace flux, many analyses are avail- 



