44 



MINERAL RESOURCES OF ALABAMA. 



able from which it may be seen that it is a rather pure lime- 

 stone, carrying normally from i to 5 per cent, of silica, and 

 from .5 to i per cent, of iron and alumina oxides, and from 

 90 to 93 per cent, of carbonate of lime, with carbonate of mag- 

 nesia varying from .75 to 3 per cent. It is hence a pure lime- 

 stone, requiring an addition of one-fourth to one-third of its 

 weight of clay or shale to make a suitable cement mixture. 



Table I. Average Composition of Trenton Limestones. 



*Trace. 



Physical Character. It is a compact blue limestone of nor- 

 mal hardness, and would therefore require more power to crush 

 and pulverize it than the softer rocks of the Selma Chalk and 

 St. Stephens limestone, but it is practically free from combined 

 water, and its use would entail no loss of heat in volatilizing 

 moisture. 



Accessibility to Clay or Shale. In all localities of the oc- 

 currence of Trenton limestone, the shales of the Coal Measures 

 are in close proximity, and, so far as these have been analyzed, 

 of suitable composition for mixing with the limestone in ce- 

 ment making. The shales from the Graves Mines below no- 

 ticed, are near the Gate City quarries, and those of the Cedar 

 Grove mines in Tuscaloosa county are close to the limestone 

 quarries at Vance. In both localities the shales are at coal 

 mines in active operation. 



