FAUNA OF ORTHAULAX PUGNAX ZONE. 5 



Vicksbiirg Group, with the Oligocene (Aquitanian) of European 

 geologists. This was announced in 189G/ and the determination has 

 since been iuWy confirmed by the vertebrate fossils studied by Osborn 

 and other paleontologists. 



With the conclusion of the discussion of the moUuscan fossils of 

 the Florida Tertiary in 1903— work to which the explorations of 

 many members of the United States Geological Survey contributed 

 material, especially Capt. Frank Burns — a review of the available 

 evidence Avas prepared and published in the last fasciculus of that 

 work.2 The arrangement of the several zones or horizons as then 

 understood was as follows, in descending order: 



1. Oak Grove sands. 



2. Chipola marls. 



3. Tampa limestone. 



4. Orthaulax bed. 



5. Chattahoochee Group. 



6. Ocala nummulitic limestone. 



7. Peninsular limestone. 



Taking these in ascending order it may be pointed out that the 

 researches of Col. Thomas L. Casey at Vicksburg, Mississippi,^ con- 

 firmed the opinion previously held by those geologists who had 

 explored the typical locality, that the Vicksburg Group as it was 

 called by Conrad (who realized that it was not faunally homo- 

 geneous^) comprises at least two faunal horizons, the upper a marl 

 containing abundant Orbitoides {Lepidocyclina) , and the lower a 

 limestone in which Orbitoides is absent or very rare. He writes 

 (p. 515) : 



The lower Vicksbnrgian consists of alternate thin strata of gray sands, 

 sandy clays, and variably, but usually loosely compacted white or gray lime- 

 stones. The upper consists of a much thinner bed of more or less red brown 

 marl, often indurated into nodular masses, or subindurated and without trace 

 of limestone, having rarely, however, thin layers of glauconitic sands and 

 comminuted shells, in which entii'e specimens when found are generally much 

 distorted by pressure. The faunas of these two beds differ very markedly, 

 and there are probably not half of the species of either common to the two.'"' 



There can be no question that we have here two faunal horizons 

 though the stratigraphy may show ho unconformity. There is very 

 little doubt that the particular species supposed by Conrad to be 



iProc. U. S. Nat. Mus., vol. 19, No. 1110, p. 30-3, 1896. 



2 Trans. Wagner Inst., voi. 3. pp. 1541-1620, 1903. 



3 Proc. Acad. Nat. Sci. Pliila. for 1901, pp. 513-518. 



* Joiirn. Acad. Nat. Sci. Phila., ser. 2, vol. 1, pp. 207-208, 1849. In this article Conrad 

 Indicates four conspicuous species which he states are found only In the lower part of the 

 bluff and not in the upper fossillferous stratum. 



^ Unpublished lists of the fossils collected by Dr. T. W. Vaughan, with close attention to 

 the stratigraphy at Vicksburg Bluff, and kindly furnished for use in the present memoir 

 show that there are of 123 well-determined species 38 peculiar to the upper bed, 27 

 peculiar to the lower bed, and 58 species found in both beds. The fauna described by 

 Conrad in 1848 comprised species from both horizons indiscriminately. 



