of Mississippi and Alabama. 33 
cannot distinguish from figures and descriptions of P. dumosum, 
but hesitate to refer to that species, since it has not been found 
in the underlying Jackson strata. Lyell mentions the occurrence 
of umosum in the lower portion of the Orbitoides limestone 
at Bettis’ Hill; the same is mentioned by Tuomey, moreover, as 
g a corres ponding position in the St. Stephens profile, 
associated with Orbitoids, and even his description of gn litho- 
logical character of the bed tallies with that of the Red Bluff de- 
posit. Hale, likewise, mentions P. dumosum as one of the prom- 
inent fossils of the “ white limestone.’ 
The uff bed seems, spunafans to be more or less coéx- 
tensive with the oe group, and re gularly associated with 
it as a subordinate feature. Its inconsiderable thickness readily 
explains its entire absence at hia points where, stratigraph- 
ically, it ought to appear. Unfortunately, the fossils accom- 
panying O. Georgiana at the only locality, other than Vicksburg, 
where it has been found in On ke have not been observed. 
The Cluiborne group proper.—That the beds of blue marl and 
white marlstone, w phe in my Sak I have designated as the 
“Caleareous Claiborne” group, are strictly equivalent to the typ- 
ical oo inthe ney at Claiborne, with underlying limestone 
e both from their stratigraphical position and the 
stein dence of all the fossils thus far observed ; though from 
the indifferent state of preservation in which the latter are foun 
in the Mississippi poten these are few in number. Ostrea sellc- 
Sormis Con. and O. divaricata Lea, are the leading shells; I ti 
also recognized Corbula ah Lea and Voluta petrosa Con. Thes 
beds possess fewer good exposures in Mississippi than either of 
the preceding groups, and may possess many unobserved features. 
Since publishing my Report, I have received evidence that it 
extends somewhat farther westward, between the territory of 
the Jackson and Siliceous Claiborne groups, than it appears on 
the map. Nor is the division between it and latter groups very 
= eae, — as the transition from siliceous to calca- 
materials a gradual one, through strata often very rich 
in 1 Soutella Tiyellé Pia Lintls Ostrea divaricata and “ a men- 
sis Tuo.? Lam not aware of the existence of any lignite bed 
in — dark colored age wuts immediately undies! thie blue 
its oa tn rv bly di ficult. I think that, as Tuomey intimates 
Am. Jour. Sc1.—Seconp Serres, Vou. XLIL, No. ‘e7—Jan. , 1867. 
5 
