22 CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



McNairy sand member. — In the vicinity of the Tennessee State line the typical beds of the 

 Ripley formation, except for a small thickness at the base, appear to merge along the strike into 

 irregularly bedded, nonglauconitic sands and subordinate clays, for the most part of shallow- 

 water origin. Their lithologic dissimilarity to the typical Ripley makes desirable a separate 

 designation for them, and the name McNairy sand member, derived from McNairy County, 

 Tenn., is proposed. This member probably reaches a maximum thickness of 400 or 500 feet. 

 The beds have yielded a few imperfectly preserved leaf remains. 



ALABAMA AND GEORGIA. 



Typical beds. — The Ripley of eastern Alabama and of the immediate Chattahoochee region 

 in Georgia resembles in all essential physical characters the Ripley of the type region in north- 

 ern Mississippi. The. total estimated thickness of the formation in the Chattahoochee region is 

 950 feet. The Ripley rests with conformable relations upon the Eutaw formation. From the 

 base upward the successively higher beds merge along the strike westward in Alabama into the 

 Selma chalk. Along the southern border of the formation in Alabama and northeastward in 

 Georgia portions of the formation, and eventually all of the formation, merge into lithologically 

 dissimilar materials. These variations from the typical materials are described below as members. 



The formation is overlain unconformably by Eocene strata. 



As in Mississippi, the typical Ripley in this region contains an abundance of invertebrate 

 fossil remains which are at many places in a fine state of preservation. Scattered fragmentary 

 vertebrate remains occur, including bones and teeth. Poorly preserved fossil leaves have been 

 discovered in marine materials at one locality. 



Cusseta sand member. — Northeast of the Chattahoochee region in Georgia the basal 200 

 or 300 feet of the formation merges along the strike of the beds into fine to coarse, irregularly 

 bedded, nonglauconitic and noncalcareous sands with subordinate clay lenses, for the most part 

 of shallow-marine, but perhaps in part of estuarine and in part of fresh-water origin. These 

 constitute the Cusseta sand member of the formation. No invertebrate fossils have been found 

 in this member. A few species of fossil leaves have been found at two localities. 



Providence sand member. — The upper beds of the Ripley formation also merge northeast- 

 ward into irregularly bedded sands and clays similar to those of the Cusseta sand member. 

 These form the Providence sand member of the formation. The thickness of this member at 

 its type section near Providence post office (now abandoned), S miles west of Lumpkin in Stew- 

 art County, is 140 or 150 feet. Northeastward from the type locality the total thickness of the 

 member increases, and the underlying typical beds of the Ripley, the "Renfroes marl" of 

 Veatch, which intervenes between the Cusseta and Providence members, becomes thinner and 

 appears to pinch out entirely in Macon County: beyond this county to the eastern extremity of 

 its areal occurrence the entire thickness of the formation appears to be made up of these two 

 members. The Providence sand is also represented west of Chattahoochee River along the 

 southern border of the Cretaceous area in Barbour, Bullock, and Pike counties, Ala. 



Xo fossil remains have been found in this member. 



SURFICIAL DEPOSITS. 



The Cretaceous deposits are overlain locally in their area of outcrop by relatively thin 

 surficial deposits, which have been disregarded in the mapping because their distribution has 

 not been determined in sufficient detail and because their representation is not germane to the 

 problems treated in this report. 



The surficial deposits consist chiefly of gravels, sands, clays, and loams. Some of them 

 occupy the uplands between the streams and belong to the class of deposits commonly referred 

 to the Lafayette formation (Pliocene?); the remainder are disposed along the sides of the river 

 valleys in the form of terrace deposits and are of Pleistocene and Recent age. Terraces are 

 well developed along Tombighee. Marion. Alabama, Coosa, Tallapoosa, and Chattahoochee rivers. 



