MOLLUSKS FROM THE TYPE LOCALITY OF THE CHOC- 

 TAWHATCHEE MARL. 



By Wendell C. Mansfield, 



Of the United States Geological Survey. 



Dr. Wm. H. Dall^ in 1892 rofen-ed the beds of true Miocene age in 

 Florida to the Chesapeake group, and recognized two subdivisions 

 which he designated the Jacksonville limestone in the eastern area 

 and the ''Ecphora bed" in the area west of the meridian of Talla- 

 hassee. The same author in 1903 wrote: 



After the elimination of the Oligocene series from the so-called Miocene of Florida 

 we have remaining practically only one series of beds which has been identified over 

 a considerable area of northern Florida. The Miocene appears as a soft limestone rock 

 in the vicinity of Jackson\dlle, and has been traced by material from artesian wells 

 on the east side of the peninsula as far south as Lake Worth . The layers of f ossiliferous 

 marl in the vicinity of Chipola River, at Alum Bluff, and other localities in western 

 Florida are usually less than 30 feet in thickness, but counting imfossiliferous clays, 

 etc., it has been estimated that the rocks of this age in Florida may have attained to 

 g_ thickness of some 500 feet or less.^ 



In 1910, Matson and Clapp ^ gave a geograpliical formational name 

 to the "Ecphora bed"* and ''aluminous clay" ^ of Dall, and say: 



In Florida the limestones, clays, and sandstones of the Miocene are lithologically 

 60 unlike the shell marls, that in the absence of satisfactory paleontologic evidence for 

 their exact correlation, it seems best to describe them separately. The two divisions 

 are therefore retained, but a new name is given to the marl. The "Ecphora bed " of 

 Dall is here called the Choctawhatchee marl, from the river in western Florida 

 where it is well exposed . At Ball's type locality the Jacksonville formation is known 

 only from well records and excavations; hence the name is not entirely satisfactory. 

 However, the United States Geological Survey has decided to retain "Jacksonville" 

 as the name of the formation. 



The Choctawhatchee marl takes its name from Choctawhatchee 

 River, where it is v/ell exposed in the vicinity of Redbay, a small 



1 Dall, Wm. n., and Harris, G. D., Neocene of North America, Biill. 84, U. S. Geol. Survey, 1892, 

 pp. 123, 124. 



2 Trans. Wagner Free Inst. Sci., vol. 3, pt. 6, p. 1594. 

 » Florida Geol. Survey, 2nd Arm. Rep., pp. 108, 114. 



< Bull. U. S. Geol. Survey, No. 84, 1892, p. 124. 



6 Bull. Geol. Soc. America, vol. 5, 1894, pp. 168, 169. 



PROCEEDINGS U. S. NATIONAL MUSEUM. VOL. 5I-N0. 2169. 



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