may be said that the lower and upper thirds of the forma- 

 tion contain 25 per cent, and upward of clayey matters 

 mixed with the calcareous material, while the middle third 

 will hold less than 25 per cent, oif these clayey impurities. 

 4, the Ripley. This, like the preceding, is a marine for- 

 mation, in which, generally, the calcareous constituents 

 predominate, but in places it contains sandy and clayey 

 beds. 



From this summary it will be seen that the Selma chalk is 

 the one of Cretaceous formations in Alabama which offers 

 limestone in such quantity and of such composition as to be fit 

 for Portland cement material. 



General description. As has been stated above, the Selma 

 chalk is a calcareous formation throughout its entire thickness 

 of about 1,000 feet. The rock, however, varies in composition 

 between somewhat wide limits, and taking account of the com- 

 position we may readily distinguish three divisions of it. The 

 rock of the upper or Portland division, is highly argillaceous, 

 holding from 25 per cent, and upward of clayey matters ; por- 

 tions of it are composed of calcareous clays or marls rather than 

 limestone, and in these beds are found great numbers of fossils, 

 mainly oysters. Along Tombigbee River these beds make the 

 bluffs from Pace's Landing down nearly to Moscow, and on the 

 Alabama they form the banks of the river from Elm Bluff down 

 to Old Lexington Landing. The strata, as exhibited in these 

 bluffs, consist of dark-colored, fossiliferous, calcareous clays, al- 

 ternating with lighter-colored and somewhat more indurated 

 ledges of purer, less argillaceous rock. At Elm Bluff, which is 

 about 125 feet high, the upper half of the bluff is of this char- 

 acter. The lower half of the bluff is composed of rock more 

 uniform in composition and freer from clay, and is the top of 

 the middle part of the Selma formation (the Demopolis divi- 

 sion), which is made up of limestone of more uniform character, 

 containing, generally, less than 25 per cent, of clayey material. 



In this middle or Demopolis division of the Selma formation 

 the fossils are rarer than in either of the others, oysters and 

 anomias being the most common forms. This variety of the 

 rock forms the bluffs along Alabama River from Elm Bluff up 

 to King's Landing. It is seen in its most typical exposure at 

 White Bluff, where it is at least 200 feet in thickness, and 



