18 CRETACEOUS D.EPOSITS OF THE EASTERN GULF REGION. 



from McNairy County, Term., is proposed. The type section of this member is exposed in a 

 cut of the Southern Railway 1\ miles west of Cypress station in this county, where the railroad 

 passes through a ridge known as "Big Hill." (See PL VI, B.) A section of this cut is given 

 below: 



Section of McNairy sand member of Ripley formation in cut on Southern Raihuay 1\ miles west of Cypress station, McNairy 



County, Tenn. 



Feet. 



6. Yellowish sandy loam, grading down into reddish argillaceous, rather coarse sand with irreg- 

 ular iron crusts along base 6 



5. Coarse, loose cross-bedded varicolored sand with scattered small white clay films and pellets 



and with irregular sandy iron concretions in upper 2 feet 17-24 



4. Coarse corrugated ferruginous sandstone presenting many parallel cavities, round to irregular 

 in cross section, of all diameters up to a foot or more, the cavities all pointing northeast and 

 southwest. Pockets of varicolored sand occur intermixed with the ironstone masses 3-10 



3. Massive, loose, fine micaceous sand, pale yellowish green in upper part and blotched and 



streaked with purple in lower part 20 



2. Irregular layer of ferruginous sandstone 1-3 



1. Pale yellowish-green, loose, finely micaceous sand with numerous thin laminse of white and 

 drab clay; toward the western end of the cut short, relatively thick lenses of black, car- 

 bonaceous clay reaching a maximum thickness of 8 or 10 feet. The black clay contains a few 

 imperfectly preserved leaf remains 25-30 



The McNairy member extends northward as a belt 5 to 15 miles in width, through Ten- 

 nessee and Kentucky, to the southern extremity of Illinois. It is correlated with the Ripley 

 formation, chiefly on the grounds of supposed continuity of strata. So far as known to the writer 

 the only paleontologic evidence throwing light on the age of the member is that furnished 

 by a single fossil found near Cairo, 111. This specimen was discovered in an excavation for a 

 bridge pier and later came into the possession of the State Museum at Springfield, 111. Thence it 

 was sent to Dr. C. A. While, at the National Museum, Washington, D. C, and was identified by 

 him as Exogyra costata Say. Recently the specimen was again sent to Washington by request 

 and was determined by the writer to be a typical specimen of Exogyra costata var. canceUata 

 Stephenson. The information given on the label accompanying the specimen is as follows: 

 "Specimen No. 835S of the State Natural History Museum, Springfield, 111. Locality: Bottom 

 of Ohio River: found in sinking a caisson for Illinois Central Railroad bridge near Cairo, 111." 

 The shell was not waterwom. Portions of the matrix in which the shell was originally em- 

 bedded, adhering to the surface, consisted of fine gray calcareous, argillaceous, micaceous 

 marine sand. Although from the account of its discovery it can not be positively asserted 

 that this specimen of Exogyra was in its original position in marine sand where found, the 

 assumption that it was in place seems reasonable. Whether this marine sand exists as a lens 

 in the predominantly shallow-water beds of the McNairy sand member or constitutes a north- 

 ward extension of the stratigraphically lower, purely marine strata of the Ripley formation 

 of Tennessee, which in Kentucky and Illinois have become overlapped and buried by the 

 beds of the McNairy member, is not definitely known. However, on the assumption that 

 the specimen belonged in place where found, the Cretaceous sea is shown to have extended, 

 probably as a broad, open embayment, as far north as Cairo. On the same assumption the 

 containing beds belong stratigraphically within the zone of Exogyra costata (see p. 23) somewhere 

 below the LiopistTut protexta subzone. 



Safford included in his Ripley certain fossiliferous beds in eastern Hardeman County, 

 Tenn., which Harris ' later showed to belong to the overlying Midway formation of the Eocene. 



Alabama and Georgia. — The time equivalents of the Selma chalk in eastern Alabama 

 and in Georgia are referred in their entirety to the Ripley formation. The strata, except 

 certain lithologic variations described below as members, are similar lithologically to the 

 typical materials of the Ripley formation of northern Mississippi. They consist in the mam 

 of dark-gray or greenish-gray more or less calcareous and glauconitic sands, sandy clays, 

 impure limestones, ami marls of marhie origin. These beds constituted the Ripley group 



' Harris, G. D., The Midway stage: Bull. Am. Paleontology, vol. 1, No. 4, 1S96, pp. 1S-22 (132-136). 



