of Mississippi and Alabama. 31 
® qipiresrts as well as resemblances, The “white limestone of 
a” has so long been quoted as the matrix of the Zeuglo- 
pa pe Ge as of the Orbitoides, that no one seemed to question 
their being contemporaries. Yet in examining all the records 
of the occurrence of Zeuglodon bones which I have been able to 
collect, I have no where “found a distinct statement that the Or- 
bitoids have been found associated with them in situ. The Or- 
bitoides limestone is mentioned as forming knolls, hill-tops— 
the Zeuglodon as being found in level fields, : or in ravines, 
The true position of the Zeuglodon bed did not, however, 
escape the glance of Lyell (On the Nummulite Limestone of 
Tistsinn., this our. [2], vol. iv); for he distinctly identifies 
the upper ‘“ Rotten limestone” bed of the Claiborne bluff with 
that which, at Bettis’ Hill, contains Aturea Alabamensis and Zeu- 
glodon, and underlies the Orbitoides rock. The only other ob- 
server who seems to pee recognized the same fact. is C. S. Hale 
(this Jour., [2] vol. vi, p. 354). ‘uomey, otherwise so accurate 
in his field’ ofervaions ignores it, and speaks only of the “ white 
limestone ” in gener: 
Nowhere has the pete more need of divesting himself of 
reliance upon lithological characters, than in the study of the 
Mississippi Eocene. Not only do the materials of the different 
groups often bear a most extraordinary resemblance to each other, 
but their character varies incessantly in one and the same stratum, 
runes short distances. Hale (/. c.) remarks that in Mississippi, A 
e Orbitoides slmesions seems to be represented by blue marl- 
sone, and so it is—sometimes. But while on the one hand we 
see the hard limestone of the Vicksburg bluff passing into blue 
marl (Byram, ay ec quarry), we on the other hand find it 
passing equally into a rock undistinguishable from that of St. 
Stephens jee re Wayne county) ; the varied fossils described 
by Conrad disappearing almost entirely, to be replaced by mil- 
lions of Orbitoids imbedded in a semi-indurate mass of carbonate 
of i tiene, magherpersd at times wah similarly constituted conglom- 
masses of Pecten Pou 
Ms pa therefore, with the lights before me, agree to the pro- 
riety of distinguishing as separate divisions the Orbitoides lime- 
stone and the Vicksburg group of fossils. Even the occurrence 
also, in the solid rock. And there are few of the characteristic 
fossils of the Vicksburg profile, which I have not on some occa- 
cone isi side by side “ea the O. Mantelli and its company ns 
en Poulsoni and Ostrea Vicksburgensis. pedi! 
of. roti the coral had i its favorite haunts—the mollusks 
There is nothing surprising in the fact that where the 
pee soy the others are usually scarce, or vice vers. 
