134 



LOWER EOCENE FLORAS OF SOUTHEASTERN NORTU AMERICA. 



sudden expansion and evolution of modern 

 types of plants after a lon<^ antecedent Cre- 

 taceous development. The floras become thor- 

 oughly modernized as compared with those 

 which preceded them, although they are still 

 very difl'erent in their general facies and dis- 

 tribution from those of the present. 



In the earliest epoch of the Eocene, known 

 as the Midway, the relations of sea and land 

 in the Gulf area difTered in only minor par- 

 ticulars from those in the late Cretaceous. 

 The waters of the Mississippi Gulf, however, 

 were deeper. This factor, combined with a 



have withdrawn southward at least as far as 

 the position indicated on the accompanying 

 sketch map (lig. 9), since terrestrial conditions 

 are shown at the extreme base of the Wilcox 

 in the most scTuthorly areas of its outcrop. 

 This interval of emergence of the embayment 

 area was followed by an equally long mterval 

 during which was laid down a great thickness 

 of deposits that are collectively known as the 

 Wilcox group. Tlie character of these sedi- 

 ments and tlieir faunas show that the Mississippi 

 Gulf was somewhat smaller in area and nuich 

 shallower than in the preceding epoch and 



FiGunE 8. — Map showing the maximum extent of the Midway transgression. 



much smaller influx of fresh water from the 

 tributary streams, owing in some measure to 

 the low reUef of the land, enabled marine 

 faunas to reach well toward the head of the 

 Gulf. These faunas indicate subtropical bot- 

 tom temperatures northward as fur as ra<lucah, 

 Ky. The known floras are very scanty and 

 unsatisfactory and in the present state of our 

 knowledge do not merit an extended discussion. 

 The maximum transgression of the sea during 

 the Midway epoch is shown on the accompany- 

 ing sketch map (fig. 8). 



The Midway Eocene was succeeded by a long 

 interval durincr which the sea is believed to 



that true marine conditions prevailed only 

 when a part of tlie Wilcox group was being 

 laid down. The shores were low and rela- 

 tively flat. They were flanked by current or 

 wave built bars and separated from the main- 

 land by shallow inlets or lagoons. The lower 

 courses of the streams were transformed into 

 shallow estuaries or broad swamps through 

 whii'h tlie smaller streams meandered. 



The maximum area of the Wilcox deposits 

 is also indicated on the accompanying sketch 

 map (fig. 9), which shows approximately the 

 shore line along which the vegetation migrated. 

 The Wilcox deposits have yielded one of the 



