68 E. W. Hilgard on Conrad's division of the Eocene. 
ArT. VIII.—Remarks on the new division i the Eocene, or Shell 
Bluff Group, proposed by Mr. Conrad ; by Eue. W. HILGar D, 
Ph.D., State Geologist of Mississippi. 
In a brief paper published in the January number of this 
Journal, Mr. Conrad proposes to distinguish, as a separate group 
of the American “Mipeane, a series of deposits but feebly repre- 
sented at Vicksburg by a five-foot stratum of dark lignitic clay 
and sand, coats in its paleontological characters from both 
the Vicksburg and Jackson group. Mr. Conrad considers it to 
be especially characterized by the occurrence of Ostrea Georgt- 
ana, and defines it as underlying the “ Orbitolite limestone of the 
Jackson Group.” He also mentions, in the section of the Vicks- 
burg Bluff, the Orbitolite limestone, as a representative of the 
Jackson group. 
The latter supposition is manifestly an oversight on the part 
of my honored friend. That the group of fos sils described by 
him, and figured in Prof. Wailes’s ‘Report, as J. sil ate do 
not occur at Vicksburg, I need not recall to his mind; but he 
has overlooked the fact that the Orbitoides Martelli thronahoue 
the state of Mississippi, at least, is entirely absent from the 
Jackson Group, the Orbitoides limestone being invariably 
accompanied by Pecten Poulsoni, Arca yeah decile Ostrea 
Vicksburgensis, and other leading Vicksburg fos 
Of Ostrea Georgiana I have unfortunately never seen an au- 
thentic specimen or description; but from the facts stated by 
Mr. Conrad, and his comparing it to P. longirostris Lamk., Iu 
hesitatingly seer u a specimens from Vicksburg, labeled 
gan. by Prof. Wailes. Upon the authority of the 
latter observer, Mr. Conrad mentions the occurrence of O. Geor- 
and 
times resembling closely G. convera of the Rotten Tigdetone. 
It is one of the leading fossils of what I have most unequivo- 
cally recognized as the upper member of the Jackson BrOuP ; it 
occurs at Jackson itself, on the hill-tops, associated with . 
glodon bones, Umbrella planulata, Cyprea fenestralis, Morio Peter- 
soni, Conus tortilis, and others, in stratum No. 7 of section 27, 
page 131 of my Report. The Jackson feuctta deseribed by Mr. 
Conrad are derived hs Nos, 4 and 5 of that section. 
