1881.] NATURAL SCIENCES OF PHILADELPHIA. 1.55 



as having an extent of 12 feet, and immediately above St. Ste- 

 phen's, was seen to dip beneath the water's edge. At this last 

 locality we have a beautiful exhibit of what has generally been 

 designated by the name of" White Limestone."' 



There can be not the least doubt, however, that this " White 

 Limestone," which has most frequently been taken to represent 

 strata of Yicksburg age, is in reality, as has been insisted upon by 

 Winchell (Proceedings of the American Association, 1850, Part 11, 

 p. 85), a combination of strata belonging to two distinct (at least, 

 as now recognized) groups of deposits. The lower moiety, 

 dipping into the river, and resting upon the subjacent Claiborne 

 sands ' Tuorne}', loc. cit., p. 157 ; Lyell, Journal Cieol. Soc, Lon- 

 don, IV, p. 15 ; Hale, A. J. Science, new ser., VI, p. 359; is the 

 true " White Limestone," an exponent of the Jacksonian group 

 of deposits, as may be inferred from its position, and the charac- 

 ter of its contained fossils,^ Moreover, were it otherwise the 

 case, it would have been very dilficult to explain the total disap- 

 pearance over a distance of only thirty miles (and with but ex- 

 ceedingly moderate dip) of the equivalent beds exposed on the 

 Alabama River at Claiborne. The upper moiety, on the other 

 hand, is a portion of the well known Orbitoide (Vicksburg or 

 Oligocene) rock, and is that which alone contains specimens of 

 Orhitoides Mantelli (Winchell, loc. cit., p. 85). 



From the data herewith presented, a section of tiie Tertiary 

 strata traced along the Tombighee River from Wood's Bluff to 

 St. Stephen's, may probably, with considerable approach to truth, 

 be constructed as follows : 



' I have been unable to discover the exact height of this bluff. Neither 

 Lyell nor Toumey mentions it ; Conrad, in the appendix to Morton's " .'Sy- 

 nopsis" (p. 23), states it is about 100 feet, 



■•' Spondylus dumosus and Oitrea panda, originally described aB charac- 

 teristic fossils of the Newer Cretaceous (upper Eocene) deposits of the 

 southern United States, have been found abundantly near the base of the 

 bluff. 



