COOKE : JACKSON AND VICKSBURG DEPOSITS 197 



section, all of which was included in the ''CoraUimestone" of 

 Smith and Johnson." The Salt Mountain section, which has 

 been considerabl}^ disturbed by folding and faulting, deserves 

 more critical study than it has yet received. 



The Byram marl is the horizon from which Conrad obtained 

 his typical Vicksburg fossils. The formation contains 6 corals 

 and 136 species of moUusks, of which 81 occur also in the Mint 

 Spring marl, 46 persisted from the Red Bluff clay (including 6 

 which have not been found in the Mint Spring marl), and 55 

 which appear to be pecuhar to the Byram marl. One of the 

 most widely distributed and abundant species is the little Sca- 

 pharca lesueuri Dall, which appears to be restricted to this 

 horizon. The recent discovery at Vicksburg of a coral which 

 T. W. Vaughan-'' reports from the fossil coral reef at Bainbridge, 

 Georgia, Tampa, Florida, and many places in the West Indies, 

 suggests a closer correlation of the Oligocene chert of Flint River 

 with the Byram marl than has hitherto been suspected. 



OUTLINE OF GEOLOGIC HISTORY 



The beginning of Jackson time was marked by a northward 

 transgression of the sea which carried the marine fauna of the 

 Moodys marl into areas in which swampy conditions had pre- 

 vailed during upper Claiborne time. This transgression was 

 most pronounced in the Mississippi Embayment where the 

 marine Jackson fauna extended into Arkansas and where the 

 Jackson flora has been recognized by Berry^^ 135 miles farther 

 north than the northernmost recognized upper Claiborne of 

 this area. The effects of this transgression are noticeable as 

 far east as Alabama River and become prominent again in 

 central Georgia, where marine deposits of Jackson age overlap 

 all older Eocene and Cretaceous strata and rest upon the crystal- 

 line rocks of the Piedmont. ^^ 



-= Smith, E. A., and Johnson, L. C, Tertiary and Cretaceous Strata of the 

 Tuscaloosa, Tombigbee, and Alabama Rivers. U. S. Geol. Survey Bull. 43 

 18-21. 1887. 



" Op. cit. 



2^ Berry, E. W., Erosion intervals in the Eocene of the Mississippi Embayment. 

 U. S. Geol. Survey Prof. Paper 95: 81-82. 1915. 



-8 Cooke, C. W., and Shearer. H. K., Deposits of Claiborne and Jackson age 

 in Georgia. U. S. Geol. Survey Prof. Paper 120-C (in press). 



