12 CRETACEOUS DEPOSITS OF THE EASTERN GULF REGION. 



Tuomey's classification. — In 1850 Tuome}' 1 described and mapped the Cretaceous deposits 

 of Alabama. Two divisions, the Lower and Upper Cretaceous, were recognized. The former 

 corresponded roughly to the Eutaw formation of the present report, and the latter included the 

 Selma chalk and Ripley formation and, erroneously, a portion of the overlying Eocene strata. 

 That part of the Cretaceous now included in the Tuscaloosa formation was erroneously referred 

 to the Tertian-. 



WincheU's classification. — In 1857 Winchell 2 subdivided the Cretaceous of Alabama in 

 descending order as follows: Prairie Bluff limestone; white sand; Rotten limestone; concrete 

 sand; loose sand; sand and clay. 



The "sand and clay," the "loose sand," and the "concrete sand" form parts of the Eutaw 

 formation of this report; the "Rotten limestone" is synonymous with the Selma chalk; the 

 "white sand" includes the glauconitic sands forming the basal portion of Prairie Bluff on 

 Alabama River, Wilcox County, Ala.; the "Prairie Bluff limestone" includes the few feet of 

 chalk rock forming the uppermost beds of the Cretaceous at Prairie Bluff. This corresponds 

 to the long, narrow tongue of Selma chalk extending through Marengo and Wilcox counties 

 above a westward-extending tongue of the Ripley formation. (See PI. LX, in pocket.) 



Hilgard's classification. — The first classification of the deposits of the eastern Gulf Coastal 

 Plain, in which the whole series of Upper Cretaceous beds was definitely assigned to that epoch, 

 was that of Hilgard, 3 State geologist of Mississippi. He differentiated four major divisions in 

 the Cretaceous deposits of that State, in descending order, as follows: Ripley group, Rotten 

 limestone group, Tombigbee sand group, and Eutaw group. 



Smith and Johnson's classification. — In 1887, Eugene A. Smith, State geologist of Alabama, 

 and Lawrence C. Johnson 4 published a classification of the Cretaceous deposits of Alabama, the 

 divisions recognized being as follows: Ripley formation, Rotten limestone, Eutaw formation, 

 and Tuscaloosa formation. 



TUSCALOOSA AND EUTAW FORMATIONS. 



East-central Mississippi. — According to Hilgard the Eutaw rests upon Carboniferous 

 rocks and includes all the Cretaceous deposits below the Tombigbee sand. He says that it 

 consists of "bluish black or reddish laminated clays, often lignitic, alternating with and usually 

 overlain by noneffervescent sands, mostly (though not always) poor in mica and of a gray or 

 yellow tint. Contains beds of lignite, very rarely other fossils." 5 



He adds: "I adopt this name (Eutaw group) hi view of these beds having been first exam- 

 ined in detail and recognized as being of Cretaceous age by Tuomey, 6 near Eutaw, Ala., where 

 they are characteristically developed." 



The Tombigbee sand, as described by Hilgard, consists of — 



A fine-grained micaceous sand, more or less calcareous, usually of a greenish tint but not infrequently gray, bluish 

 black, yellowish, and sometimes even orange-red. Clays and noncalcareous (as also at times nonmicaceous) sands 

 are also found, although generally they are only subordinate to the characteristic greenish sand, which is the exclusive 

 material in the southerly region of development, in South Monroe and Lowndes. 



The type region of the Tombigbee sand is in the vicinity of Columbus, in Lowndes County, 

 Miss., where it is mapped as a belt 15 or IS miles wide. The type exposures occur in bluffs of 

 Tombigbee River in this county. (See PI. Ill, A.) North of Lowndes County the Tombigbee 

 belt is represented as narrowing to a strip 2 to 4 miles wide, with a corresponding widening of 

 the Eutaw area. By thus narrowing the Tombigbee belt what Hilgard actually did was to 

 run his Eutaw-Tombigbee boundary line obliquely across the strike of the beds; north of this 

 line he represents strata as belonging to the Eutaw which correspond in age and stratigraphic 



> Tuomey, M., First biennial report on the geology of Alabama, 1S50, pp. 116-142. 



1 Winchell, Alexander, Notes on the geology of middle and southern Alabama: Proe. Am. Assoc. Adv. Sci., vol. 10, pt. 2, 1857, pp. 90-93. 

 J Hilgard, E. W., Report on the geology and agriculture of the State of Mississippi, 1S60, pp. 60-95. 



< Tertiary and Cretaceous strata of the Tuscaloosa, Tombigbee, and Alabama rivers: Bull. U. S. Geol. Survey No. 43, 1SS7, pp. 71-ias. 

 'Hilgard, E. \V., op. cit., p. 61. 



• Tuomey's account of the beds near Eutaw to which reference is made is recorded in the First biennial report on the geology of Alabama, 1850, 

 pp. 11S-120. Tuomey recognized the Cretaceous age of these beds but did not propose a formational name for them. 



