EARLIER TERTIARY (EOCENE AND OLIGOCENE). 731 



"Much the same interpretation must be given to this formation as has been given to tlie 

 Catahoula, for it appears that these clays, like the Catahoula sandstone, transgress several 

 biologic zones." 



Oligocene strata have not been recognized in southwestern Texas but may be present there. 



G 17, H 16-17, I 15-17, J 16. SOUTH ATLANTIC AND EASTERN GULF COASTAL PLAIN AND 



NORTH END OF MISSISSIPPI EMBAYMENT. 



The following discussion (pp. 731-745) has been compiled by T. W. Vaughan 

 from the literature and from the unpublished results of G. C. Matson and E. W. 

 Berry in western Florida, southern Alabama, and Mississippi, of E. W. Berry in 

 western Tennessee and Kentucky, and of his own researches. 



As the space allotted to this subject is limited, it is not possible to present 

 detailed descriptions of the several formations or to give geologic sections of spe- 

 cific localities or lists of the important fossils. Further information will be found 

 in the publications listed in the bibliography (pp. 840-865) under Nos. 141, 178, 179, 

 212, 214, 369, 403, 404, 405, 438, 557, 580, 583, 693, 737, 744, 751, 831, 835, 843. 

 Many of these publications contain still other citations. 



A series of reports on the Atlantic and Gulf Coastal Plain of the United States 

 is in preparation in cooperation between the United States Geological Survey and 

 the respective State surveys. These reports will present as complete discussions of 

 the different geologic formations, the geologic structure, etc., as present information 

 will permit. 



GENERAL CLASSIFICATION. 



For the Eocene formations a classification into four groups has, been adopted in the Gulf 

 and South Atlantic Coastal Plain region. The type sections of the tliree lower groups occur 

 in Alabama along Alabama and Tombigbee rivers, and that of the highest is in Mississippi. 

 These groups are the Midway, Wilcox, Claiborne, and Jackson. The marine OUgocene is 

 divided into two groups — a lower, the Vicksburg, and an upper, the Apalachicola. The former 

 takes its name from Vicksburg, Miss., the latter from Apalachicola River, Florida. The non- 

 marine Oligocene of southern Alabama, Mississippi, Louisiana, and Texas has received no 

 group name. The Catahoula sandstone and the Fleming clay of Louisiana and Texas, which 

 are mostly of upper Oligocene age, are described on pages 729-730. 



Each stratigraphic group will be described in ascending order, its distribution and variations 

 being indicated. 



EOCENE. 



Midway group.^"' — This group takes its name from Midway Landing, on Alabama River, 

 in Alabama, where it is divided into three formations.'*' The lowest, the Clayton limestone, 

 rests unconformably on the Upper Cretaceous. It is an impure limestone 25 feet thick in 

 western Alabama along Tombigbee River, but it increases in thickness to the east and along 

 Chattahoochee River includes fully 200 feet of alternating calcareous sands and limestone. The 

 Clayton limestone is overlain by the Sucarnochee clay, which on Tombigbee River is a series 

 of black or dark-brown clays at least 100 feet thick. At Black Bluff, on Tombigbee River, 

 these clays contain a few fossils but except in the lowermost strata are almost devoid of lime. 

 Toward the east, however, they become more calcareous, and in Wilcox County, east of Alabama 

 River, they form the basis of some fine black prairie lands. This formation has not been traced 

 east of Wilcox County. The Naheola forniation, which conformably overlies the Sucarnochee 

 clay along Tombigbee and Alabama rivers, is composed of 150 feet or more of gray sandy 

 glauconitic clays, containing many mariae fossils. It does not extend so far eastward as 

 Chattahoochee River. 



