EASTERN AND SOUTHERN UNITED STATES. 
149 
The following section of the bluff at Vicksburg, on the Mississippi, whence 
Conrad obtained the fossils characteristic of the Vicksburg group, described in the 
Proceedings of the Academy of Natural Sciences of Philadelphia, for October, 1847 
(and Journal of the same institution, vol. i), is given by Hilgard : 
g. Calcareous silt with snails — Bluff formation. — 10-20 feet. 
f. Bluish and yellowish hardpan, often pebbles — Orange sand. .5-20 feet. 
e. Alternating strata, 1 to 6 feet thick, of limestone and marl, containing the Vicks- 
hurg fossils, and some bands of non-effervescent gray sand and clay.— 60-65 feet. 
d. Black lignitic clay and gray sand, with Ostrea gigantea, Corbula alta, Natica 
Mississippiensis, Oytherea sohrina, Madrepora Mississippiensis.—b feet. 
c. Gray or black lignitic clays or sands, with iron pyrites ; exuding salts and sulphu- 
retted hydrogen. — 25 feet. , 
h. Solid, lustrous lignite, with whitish cleavage planes.— 3 feet. 
a. White limestone of the Jackson group 1 — 3 feet. 
The white limestone a of the above section, which “ is visible only at extraordinary 
low stages of water,” appears to be of Jacksonian age, although conclusive paleonto- 
logical evidence on this point is stiU wanting. Stratum d, containing Ostrea gigantea 
Q Qeorgiana), is that which has been identified by Conrad as corresponding to 
the Georgiana bed of Shell Bluff, on the Savannah River (“ Shell Bluff Group ”),* and 
which is erroneously stated to underlie the J ackson beds. The fossils associated with 
the large oyster in the Vicksburg Georgiana hed—CorUda alta, Meretrix sohrina, 
Natica Mississippiensis, Natica Vickshurgensis, Fidgur nodulatum, Madrepora, etc., show 
affinities alike with both the Jackson and Vicksburg faunas, and in this respect, as 
well as in stratigraphical position, would seem to point to a deposit, as has been urged 
by Hilgard, the correspondent of the “ Red Bluff” series (as restricted to the Red 
Bluff group) on the Chickasawhay. At both localities the position is immediately 
below the Orbitoides rock, but at Red Bluff Station, the large oyster is wanting. 
The relations of the Jackson and Vicksburg series of deposits to the geological 
scale have been discussed in the introductory portion of this paper. 
Grand Gulf Group (Miocene 1).— The newest Tertiary formations of Mississippi 
are constituted by the deposits of the “Grand Gulf Group” of Hilgard, which 
immediately succeed the Vicksburg beds to the south, and constitute the highest 
ridges in the southern portion of the State. “ At their lines of contact, t he Vicksburg 
* A. J. Science, new ser., xli, p. 96. 
20 JOUB. A. N. S. PHILA., VOL. IX. 
