19() COOKE : JACKSON AND VICKSBURG DEPOSITS 



The list of species collected in the Mint Spring marl includes 

 160 mollusks and 3 corals. Of these, 81 occur also in the Byram 

 marl, about 55 are found at Red Bluff or are represented there 

 by varieties, and about 66 appear to be restricted to the Mint 

 Spring marl. 



BYRAM CALCAREOUS MARL 



The type exposure of the Byram marl is in the bank of Pearl 

 River at Byram, Hinds County, Mississippi. The Byram beds 

 were supposed by Casey-^ to constitute a "sub-stage" inter- 

 mediate in age between the Red Bluff clay and the Mint Spring 

 marl, but more detailed study of the fauna shows that the marl 

 at Byram is of the same age as the upper shell bed at Vicksburg. 

 The formation consists chiefly of sandy glauconitic marl, but 

 contains also thin beds of impure limestone, clay, and sand. 

 At Vicksburg it is 42| feet thick; on Chickasawhay River incom- 

 plete exposures indicate a thickness of at least 70 feet, but at 

 intermediate places the exposed parts are much thinner. 



Overlying the Glendon limestone at several localities in Ala- 

 bama are beds of limestone, marl, and clay that appear to repre- 

 sent the Byram marl. Among these localities may be noted 

 Paynes, Salt Mountain, Gainestown,* and Choctaw Bluff (which 

 last I have not visited), in Clarke County; Castleberry, Conecuh 

 County, and Yellow River at Watkins-Henderson bridge, Coving- 

 ton County. It is probable that at least part of the exposure at 

 Natural Bridge, Walton County, Florida, represents the same 

 horizon. The upper 60 feet or more of the section at Salt Moun- 

 tain probably includes the Byram marl, but as the two species 

 of corals in the limestone at the top are found elsewhere in 

 deposits of Chattahoochee age^'* part of the section may be 

 younger than the Byram. The Glendon limestone member and 

 perhaps also part of the underlying "chimney rock" of the 

 Marianna limestone are represented in the lower part of the 



23 Casey, T. L., Philadelphia Acad. Nat, Sci. Proc. 53: 517-518. 1901. 

 2^ Vaughan, T. W., Tertiary corals from Central America, Cuba, and Porto 

 Rico. U. S. Nat. Mus. Bull. 102 (in press). 



