THE PHYSICAL CONDITIONS AND AGE INDICATED BY 



OF THE ALUM BLUFF FOMIATION. 



THE FLORA 



By Edwakd WiLBKR Berry. 



INTRODUCTION. 



Tlie present paper has for its purpose the 

 description of a small ilora collected from the 

 Alum Bluff formation, representing a horizon 

 hitherto unrepresented paleobotanically in 

 southeastern North America, and the discus- 

 sion of the beai'ing of this flora on the physical 

 conditions of deposition and the probable age 

 of the deposits. 



GEOLOGY OF THE DEPOSITS. 



The ^Uum Bluff formation was named from 

 the bluff of that name on the east bank of the 

 Apalachicola River, about 25 miles l)elo\v Chat- 

 tahoochee or River Junction, in Liberty County, 

 Fla.i (See PI. vii, B, p. 56.) It is, according 

 to present knowledge, the uppermost formation 

 of the Apalachicola group. It comprises three 

 membci's, which, named in ascending order, are 

 the Chipola marl member, the Oak Grove sand 

 member, and the Shoal River marl member. 



The Chipola marl, which is a thin yellowish 

 clay marl at the base of the formation as defined 

 by Matson and Clapp, caiTies a very extensive 

 and well-preserved marine fauna. It was 

 named from Chipola River, in Calhoun County, 

 Fla. The Oak Grove sand, stratigraphicall}' 

 mtermediate between the Chipola and Shoal 

 River, is a thin, highly fossilifcrous gray or 

 greenish fine sand named from Oak Grove, on 

 Yellow River, and not represented by a litho- 

 logic unit at Alum Bluff. The Slioal River 

 marl, the highest known fossiliferous member 



' The geology of this region is lully discussed in the following publica- 

 tions: 



Matson, G. C, and Clapp, F. G., A prelimiuair report on the (jeology of 

 Florida: Florida Geol. Survey Second Ann. Kept., pp. 21-173, 1909. 



Vaughan, T. W., A contribution to the peoIo;;ic history of the Floridian 

 Plateau: Carnegie Inst. Washington Pub. i:!3, pp. 99-185, 1910; see also 

 U. S. Geol. Survey Prof. Paper 71, pp. 741-745, 1912. 



of the formation, is a thin series of interbedded 

 greenish sands and marls overlying the Oak 

 Grove sand. It was named from Shoal River, 

 in western Florida, and is not represented by a 

 lithologic unit at Alinn Bluff. 



The following section was taken at the point 

 where the fossil plants were collected, near the 

 lower end of the bluff and in the immediate 

 vicinity of the section measured by Dall.- It is 

 deemed worthy of reproduction because it 

 differs in certain particulars from Dall's sec- 

 tion. Still other sections from different parts 

 of the bluff are given by Sellards and Gunter.' 



Section at Alum Bluff, Fla. 



Pleistocene (?): rect. 



Light-colored ferruginous, rather loose sands. 9 



Hard reddish clay 2 



Variegated reddish and yellowish ferruginous 



sands 0-5 



Miocene: 



Ohoctawhatchee marl: 



Dark-gray p\Titiferousclay, moreor less carbo- 

 naceous but scarcely meriting the term lig- 

 nitic given to it by Langdon, as no lignite 

 or plant fossils were obser\ed in it. Traces 

 of in\-ertebrate fossils, for the most part un- 

 determinable, were obser\ed in places. 

 The pyritiferous character of the clay gives 

 it an alum-like taste, wliich accounts for the 

 name of the bluff . Approximate thickness. 25 

 Bluish (when unweathered) fossiliferous clay 

 marl of irregular tliickness, canying Muli- 

 nia cowjesta, Ecphora quadricostata, Turri- 

 tella rariahilis, and other species; much o.xi- 

 dized in its upper portion, in whirh the fos- 

 sils are represented liy poor casts, ow'iug to 



the solution of the sliell substance 15-30 



Erosion unconformity. 



~ Dall, W. H., and Stanley-Brown, J., Cenozoic geology aloug the 

 Apalachicola River: Geol. Soc. America Bull., vol. 5, ji. 157, 1S94 



s Sellards, E. H., and Gunter, Herman, Florida Geol. Survey Second 

 Ann. Rept., pp. 275, 276, 1909. 



41 



