44 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 



fossil species that have been described many 

 occur in associations that are obviously tem- 

 perate in character. 



To summarize the climatic conditions indi- 

 cated by the flora, they are those C)f a tropical 

 flora becoming replaced by a temperate flora, 

 namely, subtropical or very warm temperate. 

 These conditions are obviously different from 

 those indicated by the Chipola marine faxma, 

 which comprises over 400 knowni species, mostly 

 Mollusca, and indicates a shallow sea (maximum 

 depth not over 20 fathoms) and, according to 

 Vaughan,' strictly tropical temperatures — that 

 is, the bottom temperature of the water did 

 not go below 70° F. dm-ing the year. 



As has already been indicated, the flora em- 

 braces a number of tropical types which, as is 

 shown by the existing flora, are legitimately to 

 be expected to extend more or less beyond the 

 equatorial belt in areas where rainfall is abun- 

 dant and where extremes of low temperature 

 are absent. Associated with these are forms 

 like Ulmus, whose modern representatives are 

 prevailingly north temperate but some of which 

 extend into boreal regions. Still other of the 

 Alum Bluff forms, the Rhamnus, Bumelia, and 

 Diospyros, represent families wliich are mainly 

 tropical in the existing flora but which as repre- 

 sented by these genera have extended over large 

 areas of the warmer parts of the Temperate Zone. 



It seems to me that among existing plant 

 assemblages the Alum Bluff flora represents 

 three types of plant associations. One corre- 

 sponds in a general way to the "low hammock"' 

 of present-day peninsular Florida, a type inter- 

 mediate between the true hammock and the 

 swamp type. A second plant assemblage indi- 

 cated is that of the low-lying semiswamp pal- 

 metto-brake type, along with some forms of the 

 sandy strand, such as Pisonia, Cjesalpinia, and 

 Fagara. In other words, this flora would find 

 a congenial habitat at the present time in the 

 delta of Apalacliicola River or almost any- 

 where along the coast of peninsular Florida. 

 Although so much less extensive, the Alum 

 Bluff flora is somcwliat less tropical in its f acies 

 than the flora of the Wilcox group and decid- 

 edly less tropical than the floras of the Clai- 

 borne, Jackson, Vicksburg, or Catahoula. On 

 the other hand, it has not nearly the temperate 

 facies of the flora of the overliving Chesapeake 



'Vaughan. T. W., Carnegie Inst. Washington Pub. 133, p. 



156, 1910. 



Miocene and also indicates much more humid 

 conditions than the latter. This statement is 

 based on the flora of the Calvert and a consid- 

 eration of the abundant marine faunas of the 

 Calvert, St. Marys, Yorktown, Duplin, Clioc- 

 tawhatchee, and Jacksonville formations. 



The Alum Bluff flora may be considered to 

 be the result of a reversal of the history of the 

 present flora of peninsular Florida. That is to 

 say, the present flora represents primarily a 

 temperate flora receiving additions from the 

 Tropics, whereas the Alum Bluff flora repre- 

 sents an endemic tropical flora gradually becom- 

 ing invaded by members of a temperate flora 

 as a result of changing climatic conditions. 



AGE OF THE FLORA. 



The stratigraphic relations clearly indicate 

 that the Alum. Bluff flora is younger than the 

 Vicksburg Oligocene and older than the Chesa- 

 peake Miocene. The faunal and floral evidence 

 is equally conclusive. Not a single Alum Bluff 

 plant is common to the Oligocene (Vickslnirg 

 and Catahoula) floras of Mississippi, Louisiana, 

 and Texas nor to the Chesapeake Miocene floras, 

 which are, however, smaller than those from the 

 Oligocene. Moreover, the facies of the Alum 

 Bluff flora is decidecUy different from that of the 

 floras of any of these horizons. There are no 

 western United States or West Indian fossil 

 floras for comparison, so that it remains to con- 

 sider the probable European ecpiivalents of the 

 Alum Bluff. 



As the Alum Bluff flora is obviously younger 

 than the abundant European floras of the San- 

 noisian (Lattorfian, Tongrian) and Stampian 

 (Rupelian) and older than the exceedingly rich 

 floras of the Helvetian and Tortonian (Vindo- 

 bonian) , the only stages remaining are the Chat- 

 tian (Kasselian), Aquitanian, and Burdigalian 

 (Langhian , Mayencian ) . 



The Chattian (Fuchs, 1894) is the lower 

 Aquitanian of Munier Chalmas and De Lappa- 

 rent (1893). It is considered the equivalent of 

 the Kasselian and in the Paris Basin is repre- 

 sented, according to Lemoine, by the meulieres 

 de Montmorency. According to Hang its in- 

 vertebrate fauna is distinguished by the absence 

 of Miocene types. 



The Aciuitanian (Mayer, 1857) now has the 

 nari-ow limits assigned by DoUfus (1906-7). It 

 marks the maximum regression of the Oligocene 



