LOWER EOCENE FLORAS OF SOUTHEASTERN NORTH AMERICA. 



133 



PHYSICAL CONDITIONS. 



No part of Xdrth America is so fiiv<>r;il)ly 

 situated for the study of the floras whieii pre- 

 ceded tli(> present, extending back to the 

 first recorded appearances of angiospenns, as 

 the South Atlantic and Gulf States. No sin- 

 gle part of North Anieri(ui contains so continu- 

 ous a series of Tertiary deposits that. <'arry 

 fossil jilants. In this area are found abundant 

 floras in the lower and middle parts of the 

 Eocene, a small flora in the upper Eocene, 

 large floras in the Oligocene, some material in 

 tiie later ]\liocene, and rather abundant ft>ssil 

 plants in the Pliocene, as well as in many 

 Pleistocene deposits. The Rooky Mountain 

 region is rich in Eocene fossil plants and con- 

 tains some Miocene floras, but practically no 

 Oligocene or Pliocene floras. The Pacific 

 coast region likewise furnishes Eocene and 

 Miocene fossil plants but none of Oligocene age. 



The fossil floras of the Coastal Plain occur 

 in an area in which some measm-e of accura<'y 

 can be attained in ]iredicating the general char- 

 acter and course of ocean currents and winds 

 and other physical features of the environ- 

 ment. On the other hand, the western floras 

 just mentioned grew in areas wher'e at times 

 the effects of volc.uusm were great; in areas 

 where erogenic movements were active and 

 where numerous changes in topography that 

 involved elevations of several thousands of 

 feet are recorded; areas in which climatic 

 conditions not only differed from place to 

 place but passed through a large cycle of 

 secular changes. All these factors greatly 

 complicate the floral history. 



The floras of the southern Coastal Plain are, 

 moreover, checked for the most part l)y very 

 ahundaiit marine faunas that are contained in 

 intercalated ])eds, or else the plant-tx^ariiig 

 beds, which represent the coastal swamps and 

 the shaflow-w'ater deposition of the old em- 

 bayment, merge laterally into the contempo- 

 raneous limestones or marls whicli wei-e form- 

 ing in more open waters along the coasts to 

 the south, so that evidence regarding land 

 temperatures, derived from the llora, can Ix' 

 compared with evidence^ regarding depth, 

 character of the l)ott()m, and marine tempera- 

 tures derived from the sedimentary rocks 

 a!id their faunas. These criteria have been 

 admiraldy worked out for the Morida area by 



DaU and Vaughan for the post-Eocene, and 

 their results furnish a reliable basis for deduc- 

 tions from the study of fossil Ihu-as of that age. 



With the exception of fragments of the pet- 

 rified stems of conifers, palms, and dicotyle- 

 dons the plant remains occur in the form of 

 impressions, mostly of foliage, though ihcro. is 

 a goodly representation of fruits and seeds, 

 and even a few flowers have been preserved. 



Though the oscillations of the embayment area 

 have been numerous, their amount, as I have 

 just mentioned, has been inconsiderable, oidy a 

 few hundred feet at most, and the coastal re- 

 gion has uniformly been one of slight relief. 

 Tlie floras show an almost complete absence of 

 upland types, which is in striking contrast to 

 the European older Tertiary floras. Europe, 

 the only large area of the globe which has been 

 thorougldy studied, was far less stable than 

 this region in Tertiary times, and as it lay 

 much farther toward the pole it was subse- 

 quently subjected to the rigors of Pleistocene 

 conditions, whose influence never i-eached our 

 Southern States. 



The paleobotanic record of the Atlantic and 

 Gulf Coastal Plain furnishes a history which 

 extends back beyond the oldest known an- 

 giosperms to a time (Lower Cretaceous) when 

 the flora was made up almost entirely of tree 

 ferns, conifers, and those interesting cycado- 

 phytes (Cycadeoidea) whose trunks are in 

 places preserved with such marvelous perfec- 

 tion that the outlines of the embryos in the 

 ovules can commonly be made out in detail. 

 To come a step nearer my present theme, a 

 step of some milhons of years, from the Lower 

 into the Upper Cretaceous, we find tlie first 

 great modernization of the floras of the world, 

 which was due to the seemingly sudden evolu- 

 tion of the main types of angiosporms. These 

 Upper Cretaceous floras are weU represented in 

 the Coastal Plain from Marthas Vineyard to 

 Texas. They extend northward to Gi'eeidand 

 and southward to Argentina in South America 

 and indicate very different physical conditions 

 from those which prevail at the present time. 

 1 do not intend, however, to dwell on the Upper 

 Cretaceous floras in this coimection, but pass 

 to a consideration of the succeeding EociMie 

 cjjoch of plant evolution. 



The Eocene, as defined ])y Lyell, was marked 

 by the dawn of the recent species of marine 

 Mollusca. It is cfiually well marktul by the 



