148 
THE TERTIARY GEOLOGY OP THE 
eitlier sucli reference lias been based upon error, or that tlie interassociation, where it 
actually exists, dates to a period subsequent to that of the original deposition of the 
strata. At any rate, the painstaking investigations of the geologist last mentioned, 
have failed to reveal a single instance where an “ Orbitoid has been found associated 
with either the Zeuglodon, or any of the characteristic fossils of the Jackson group.”* 
From the neighborhood of Jackson, on the Pearl River, Conrad, in 1855, described 
the series of fossils which led him to institute a distinct division of the Eocene under 
the name of the “Jackson,” and which he correctly located between the Claiborne 
and Vicksburg beds. Of the forty species described from this locahty f thirty-four 
were considered to be peculiar, and only five — Rostellaria velata, R. staminea, Scalaria 
misfiula, Pscudoliva vehisia, and Endapachys expansum — common to the Claiborne 
series. None of the Vicksburg fossils were considered to be represented. From the 
nature of his collection, which was a selected one, Conrad was led to infer that a far 
greater dissimilarity existed between the Jackson and Claiborne series on the one side, 
and the Jackson and Vicksburg on the other, than the actual facts warranted. In 
addition to the Claiborne fossils already mentioned as occurring in the Jackson beds. 
Prof. W. 1). Moore J mentions Cardita planicoata and Gardita rotunda; and as 
common to the ^’icksburg series Cardita rotunda, NavicuJa {Area) lima, Cytherea 
sofjrina, C. imiiahiHs, Mactra fanerata, Psammohia lintea, Turhinella Wilsoni, Cypraa 
Hntea, C. spJarroides, Nafica Viekshnrgensis, and Dentaliuni Mississippiense. § 
That a much closer connection exists between the deposits of the Jackson and 
^hcksburg scries than was supimsed by Conrad is proved by the character of the 
fossils occurring at or near Red Bluff Station, on the Chickasawhay River, in deposits 
lying intermediate' between the Jackson and the typical Vicksburg, and considered by 
llilgard to repre-st'nt a subordinate group (Red Bluff Group) of the Vicksburg series. 
Of twenty siH'cifically identified forms, || Prof. Moore enumerates ^ four,— 
2>hiuicosta, Clacelithes hamerosas ?, Rostellaria velata and Flahellum Tfe/tfesfi— as 
iH-mg common to the Jackson beds, and twelve to the Vicksburg- CarchVa rotunda. 
Card, urn dnu^rsurn, Falgoraria Mississippiensis, Turhinella protraeta, T. perexilis, 
JU,a>mum M,ssm,pjriensis, Cassidaria lintea, Mitr a Mississippiensis, Busycm spiniqer. 
Conus saundens y, Natica sigaretina and N. V ichsburgensis 
* A. .T. Science, new ser,, xliii, p. 30. 
fomjveo-imj,era^tly described and Hlentiflcation from scanty materials, especially in the case of 
Oardimn ditersum, Rostellaria velata, Fnlgoraria Missis- 
(^uUirui linUa, Mitra Missisi,^itusU Conus sau^rn spiaiger, Buccinum Mississim'ense, 
and M. sigaretina, 
