■|90, 91, 92] HYDRAULIC LIMESTONE. fy'i 



and 11 E., and in the hilly country intervening between the two creeks — whera^ 

 however, even deep wells frequently terminate in the gray laminated clay of the 

 Eutaw group. 



USEFUL MATERIALS OF THE CARBONIFEROUS FORMATION. 



90. These consist of Limestones, both common and hydraulic, 

 Sandstones, and materials for Class. Bituminous coal is not to 

 be looked for, since the strata appearing in Mississippi cor- 

 respond to those underlying the Coal Measures in Alabama and 

 elsewhere ; so that by mining in them, we should recede from, 

 instead of approaching to, the level at which the coal is always 

 found. According to the geological map of Alabama, the rocks of 

 the Coal Measures of the Warrior coal field approach nearest to 

 (within 7 or 8 miles of) the Mississippi line, in Marion county, Ala.; 

 but I am not aware whether the coal itself extends so far. 



91. Hydraulic Limestone. — The dark-colored (black or gray) 

 slaty rock, which occurs near Eastport, and which may be looked 

 for, more or less, all over that part of the region colored black on 

 the map, which lies N. of the line between TT. 2 & 3, possesses 

 strongly hydraulic properties; i. e. it does not slake after burning, 

 like common limestone, but if pulverized and then wetted, will 

 harden under water, like Portland or Roman Cement. This prop- 

 erty is imparted to the limestone by the clayey impurities which it 

 contains, and in imitation of this natural mixture, hydraulic 

 cement is now sometimes prepared, either by treating in the same 

 manner as the rock naturally occurring, an intimate mixture of 

 clay and lime, artificially prepared, or by mixing with quicklime 

 certain substances naturally occurring (such as the puzzolana of 

 Italy) in a finely ground condition. These artificial cements, 

 however, are rarely equal to those prepared from good natural 

 hydraulic limestone. 



The principal localities of occurrence of this rock thus far ob- 

 served, have been mentioned above (1F81). 



92. The rock which forms the bald hilltops on the right bank of 

 Yellow Creek, at Billing's mill, S. — , T. 1, R. 10 E., (and which 

 may probably be found in many similar positions in the hilly coujq- 

 try lying between the Red Sulphur Springs and Eastport road, 

 and the Tennessee River), I have found to be of very superior 

 quality ; the cement made of it sets almost as rapidly as plaster of. 



