THE RELATION BETWEEN THE DUNNELLON FORMA- 

 TION AND 1 HE ALACHUA CLAYS OF FLORIDA. 



E. H. SELLARDS. 



The term "Alachua Clays" was proposed by Dr. VV. H. Dall 

 in 1885 for the clay beds in the vicinity of Archer from which at 

 that time extensive collections of vertebrate fossils were being made. 

 The hrst published account in which this term was used, however, 

 is found in Bulletin 84 of the United States Geological Survey, 

 page 127, 1892. The formation is there described as occurring in 

 sinks, gullies and other depressions in the Upper and Lower Oligo- 

 cene (then regarded as Aliocene and Eocene respectively). The 

 clays were considered by Dall as representing a remnant of a previ- 

 ously more extensive formation. Although in his original descrip- 

 tion, Dall mentions a number of localities, including those on Peace 

 Creek, Caloosa Piver and rock crevice's at Ocala, now known to be 

 ^ of later date, yet the deposits are sufficiently characterized by the 

 description of the exposures in the vicinity of Archer which are re- 

 garded as the typical localities. 



The term "Dunnellon formation" was first used by the writer 

 m 1910 to designate the extensive deposits which hold the hard 

 rock phosphates of Florida. While the prevailing phase of the Dun- 

 nellon formation is light gray phosphatic sands, the deposits include 

 also local beds, lenses, or masses of clay, as well as phosphate rock, 

 flint boulders, pebble conglomerate and limestone fragments. 



A recent examination of typical localities has convinced the 

 writer that the Alachua Clays and the Dunnellon formation are not 

 separable, the former representing, in fact, a local phase of the 

 latter. The Dunnellon formation, as I have elsewhere shown, has 

 accumulated from the residue of the formations that have disin- 

 tegrated in situ, the material having been reworked to a consider- 

 able extent, through the agency of the sinks, sink hole ponds, small 

 lakes and local streams that existed in this area during the earlier 

 stages of its physiographic development.* 



*Fla. Geol. Surv. Third Ann. Report, p. 32, igio; and Fifth Ann. Re- 

 port, pp. 53-56. IQ13. 



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