30 E. W. Hilgard on the Tertiary formations 
a the transfer of the latter to the Jackson group. (This Jour. * 
an., 1866.) 
with bite ore bones, x hla Se oie oe a eae ee ee 
€ 
Vicksburg marl and limestone. Nowhere in Mississippi has 
a single phage been found associated with either the Zeuglo- 
on, or any of the characteristic fossils of the Jackson group. 
It is quite possible that in Alabama, Zeuglodon bones may have 
been picked up in company with Orbitoids, equally as well as 
with drift pebbles. There, the same ravine often cuts into the 
na 
single panes elsewhere, the regions in which the several 
groups crop out are so aa ‘separated geographically, (in conse- 
quence of the intercalation of lignitic strata,) as to leave the ob- 
server no legitimate chance of error in reference to fossils. 
Notwithstanding she defectiveness of his materials, Conrad 
assigned to the Jackson group its proper place, between that rep- 
resented by the Claiborne sands and the Orbitoides limestone. 
He still, however (/. c.) thought it most peony that the Zeu- 
glodon was referable to the same age as the lat 
A great deal of the obscurity in 1 which ne Elative age of the 
Southwestern Tertiary has been involved, is owing to too great 
a reliance placed by most observers on Hichalogioal characters, 
* Tt is impossible to avoid erroneous infe ne from the Repa.go aoe fd fossils 
sent for determination by a and er y collected with a view »m plete- 
ness, or general results. From the collection of Jackson gerge ubm ited § to Mr. 
Conrad, any one would infer that this rich fauna had been totally extinguished 
some cataclysm, before tl eposition of the + Vicksborg strata ; whereas in fact, 
probably more than one-fifth of the former fauna is represented in the la 
‘The same has happened with reference to the superior Cretaceous of Miseise issippi 
and Alabama, the Ripley group of Conrad, whose fossils as described by him from a 
selecte 
lection im, would seem to constitute an isolated group, 
al pecifically, with the lower members of the of t 
, gene i and el whereas in reality it shares the leading fossils of the lat- 
and is connected with the Rotten Limestone group especially, by transitions 
both lithological ~— paleontological, as ascertained by myself a year prey 
(Misa. Rep.. pp. 79, 84.) 
