79 



the rocks of this division, while above Roe's, at Jordan's, occurs 

 the line of junction of this with the middle division. Near this 

 line of division there is a very characteristic feature to be ob- 

 served at many points, viz., about 10 or 15 feet below the hard 

 lulges cf pure limestone forming the base of the middle 

 (Demcpolis) division the dark-colored argillaceous rock shows 

 a tendency to flake oft" and weather into caves, sometimes to be 

 seen for long distances along the bluffs, as on Alabama River 

 just above King's Landing, on the Tombigbee below Roe's 

 Bluff, and at Jordan's Ferry. This peculiarity is illustrated in 

 Plate IT. The outcrop of the argillaceous rocks of this division 

 gives rise to black prairie soils, in which beds of fossil shells, 

 mainly oysters, are common. 



It has been suggested that the: argillaceous rocks of this and 

 the uppermost division could be mixed with the purer limestone 

 of the middle division in such proportions as to constitute a 

 good cement mixture. In this case it would be easy to select 

 localities near the junction of the two divisions where both va- 

 rieties of the rock could be quarried, if not in the same pits, at 

 least in pits closely adjacent. This would do away with the 

 need of adding other clay to the limestone. Localities of this 

 sort would be found along the border north and south of the 

 belt of outcrop of the white Demopolis rock. 



Details of localities. The general characters of the rock of 

 this formation have been mentioned above, and it remains to 

 give details of the special localities examined, together with 

 analyses of the limestones collected. In making the collections 

 material from the middle or Demopolis division of the forma- 

 tion has been generally chosen, since most of the limestone of 

 the formation which contains 75 per cent, and upward of car- 

 bonate of lime is to be found in this division. At the same time 

 specimens of the more argillaceous material, especially O'f the 

 lower (Selma) division of the formation, have been taken for 

 comparison and analysis, with a view to ascertaining whether 

 or not it will be practicable to provide a cement mixture by 

 using the proper proportions of the purer and 1 more argillace- 

 ous materials. 



Inasmuch as suitable material for cement manufacture can be 

 had in practically unlimited quantity all along the outcrop of the 

 pure limestone of the Demopolis division, the location: of the 

 plants for the manufacture of this product will be determined bv 



