SUMMARY OF PRESENT CLASSIFICATION. 19 



of Langdon * except that he included hi the division an additional 120 feet of strata at the 

 base of the series, which are here, on paleontologic grounds, correlated with the Tombigbee 

 sand member of the Eutaw formation. 



The Ripley formation of the Chattahoochee region is divisible paleontologically on the 

 basis of the ranges of the contained species of Exogyra exactly in the same manner as -was stated 

 to be true of the Selma chalk. The lower part, embracing the lower one-third to one-half of 

 the formation, is characterized by the presence of Exogyra ponderosa Roemer and Exogyra 

 ponderosa var. erraticostata Stephenson; the upper, embracing the remainder of the formation, 

 is characterized by the presence of Exogyra costata Say. The formation contains a large number 

 of invertebrate species which range from the base, or even from below the base of the formation, 

 to its top, and it contains also a number of species with restricted ranges, some confined above 

 and some below the horizon separating the two types of Exogyra. Typical exposures of the 

 Ripley strata are shown in Plate VII, A, B. 



Northeastward from Chattahoochee River hi Georgia the equivalents of the Ripley forma- 

 tion pass first into a series of alternating marine and shallow-water beds and still farther north- 

 eastward into irregularly bedded sands and clays of shallow-water origin, overlapped and 

 concealed in central and eastern Georgia by Eocene beds. 



The classification of the Georgia Cretaceous deposits adopted by Otto Veatch in 1909 2 is 

 essentially the same as that of Langdon, except that Veatch subdivided the Ripley into four 

 parts — Blufftown marl, Cusseta sand, Renfroes marl, and Providence sand — on the basis of the 

 alternation of beds of marine and shallow-water origin recognizable in a part of the area. 



A part of the ' 'Blufftown marl," as previously explained, is here correlated with the Tombig- 

 bee sand member of the Eutaw formation. The remainder of the "Blufftown" and the "Ren- 

 froes marl" are lithologicaUy indistinguishable from the typical Ripley and require no separate 

 designation. 



The basal part of the Ripley formation, embracing 200 or 300 feet of strata, merges north- 

 eastward from the Chattahoochee region into irregularly bedded, nonglauconitic sands with 

 subordinate lenses of clay, probably in part of shallow marine, in part of estuarine, and in part 

 of fresh-water origin. These constitute the Cusseta sand member of the formation. (See PI. 

 VIII, A.) 



The upper part of the formation also merges northeastward along the strike into irregu- 

 larly bedded sands and clays similar to those of the Cusseta sand member. This is the Provi- 

 dence sand member of the formation. A typical exposure is shown in Plate VIII, B. At its type 

 section near Providence post office (now abandoned) about 8 miles west of Lumpkin, Stewart 

 County, the member has a total thickness of 140 or 150 feet. The Providence sand is also 

 represented west of Chattahoochee River along the southern border of the Cretaceous area in 

 Barbour, Bullock, and Pike counties. It is believed that the top of the Providence sand member 

 occupies a slightly higher stratigraphic position than the top of the Cretaceous farther west hi 

 the eastern Gulf region. 



Both the Cusseta sand member and the Providence sand member increase hi thickness 

 northeastward, whereas the intervening typical beds of the formation, the "Renfroes marl" of 

 Veatch, become gradually thinner, and eventually hi Macon County appear to pinch out entirely. 

 The entire thickness of the formation beyond this point to the east is apparently represented by 

 the Cusseta and Providence members. 



SUMMARY OF PRESENT CLASSIFICATION. 



GENERAL SEQUENCE. 



The areal distribution of the several formations and members recognized hi tne eastern Gulf 

 region is shown on the geologic map (PI. IX, in pocket) . Then stratigraphic positions, lithologic 

 variations, and age equivalencies, are graphically represented in the diagram, Plate X. 



An unconformity of regional extent separates the Lower Cretaceous deposits from those of 

 Upper Cretaceous age. The Upper Cretaceous deposits are believed to form hi the mahi a 



1 Langdon, D. W., jr., Variations in the Cretaceous and Tertiary strata of Alabama: Bull. Geol. Soc. America, vol. 2, 1891, pp. 5S7-606. 

 ■ Veateh, Otto, Second report on the clay deposits of Georgia: Bull. Geol. Survey Georgia No. IS, 1909, pp. 82-106. 



