SUMMARY OF PRESENT CLASSIFICATION. 21 



Tombigbee sand member. — The Tombigbee sand member consists of massive, glauconitic, 

 more or less calcareous and argillaceous sand. Through Georgia, Alabama, and east-central 

 Mississippi it constitutes the upper 100 to 200 feet of the formation. In northern Mississippi 

 it thickens above, embracing within its stratigraphic limits beds which are the time equivalents 

 of a portion of the overlying Selma chalk. 



Marine invertebrate fossils are common in the lower and upper parts of the member in the 

 Chattahoochee region and are numerous in the upper 50 or 75 feet of strata in Alabama and 

 in east-central Mississippi; they occur also at several horizons in the thickened portion of the 

 member in northern Mississippi. The teeth of fishes, particularly those of sharks, are numerous 

 in the uppermost beds of the member in Alabama and in east-central Mississippi, and with 

 them occur other scattered, fragmental, vertebrate remains. 



Coffee sand member. — The Coffee sand member consists predominantly of glauconitic sands 

 characterized by irregularity of bedding and by the presence of thin lamina? and thinly laminated 

 layers of dark clay. The beds are the Tennessee representatives of the thickened portion of 

 the Tombigbee sand member of northern Mississippi, which in turn represents the time equivalent 

 of the basal portion of the Selma chalk. (See PI. X.) The division has an estimated maximum 

 thickness of 200 to 300 feet. The beds contain an abundance of comminuted plant fragments 

 and scattered pieces of lignite. The member has yielded one identifiable fossil leaf, Salix 

 eutawensis Berry (identified by E. W. Berry). (See p. 26.) 



SELMA CHALK. 



The Selma chalk consists in the main of more or less argillaceous and sandy limestones 

 rendered chalky by their large content of foraminiferal remains, with interbedded layers of 

 nearly pure, hard limestone at wide intervals. In western Alabama the terrane has a measured 

 maximum thickness of 930 feet as determined by the record of a well at Livingston, in Sumter 

 Count y. The formation rests conformably upon the Eutaw formation, and where it attains its 

 maximum development in western Alabama and in east-central Mississippi is overlain uncon- 

 formably by Eocene strata. 



The chalk beds merge along the strike in either direction into nonchalky equivalents, which 

 in northern Mississippi and Tennessee are included in part in the Tombigbee and Coffee sand 

 members of the Eutaw formation and in part in the Ripley formation, and in eastern Alabama 

 are included entirely within the Ripley formation. 



In addition to Foraminifera, the chalk beds contain invertebrate fossils in greater or lesser 

 abundance throughout their vertical and horizontal extent, the most conspicuous of which 

 belong to the families Ostreidse and Anomiidse. Fossils are especially abundant in places in 

 the impure, argillaceous phases of the terrane and weather out in great numbers. (See PI. XI, 

 A, B.) The chalk also contains scattered sharks' teeth and other fragmental vertebrate remains. 



RIPLEY FORMATION. 

 MISSISSIPPI. TENNESSEE, KENTUCKY, AND ILLINOIS. 



Typical beds. — The typical beds of the Ripley formation consist of more or less calcareous 

 and glauconitic sands, sandy clays, impure limestones, and marls, of marine origin, reaching an 

 estimated maximum thickness in this region of 250 to 350 feet. The formation rests with con- 

 formable relations in part upon Paleozoic rocks, in part upon the Eutaw formation (in Ten- 

 nessee), and in part upon the Selma chalk. From Tennessee and northern Mississippi south- 

 ward the successively higher beds merge along the strike into the chalky limestones of the Selma 

 formation. Northward the typical beds of the Ripley formation are believed to merge hori- 

 zontally into a series of sands and clays of shallow-water origin, to which the name McXairv 

 sand member is given. The formation is overlain unconformably by Tertiary beds of Eocene age. 



The typical beds of the Ripley formation contain in many places an abundance of inverte- 

 brate fossil remains, some of which are in a remarkably perfect state of preservation. Sharks' 

 teeth occur scattered sparingly through the deposits, which also contain a few fragments of 

 bones. 



