i9'i-] ATLANTIC AND GULF COASTAL PLAIN. 305 



sippi Gulf were, however, deeper. This factor combined with a 

 much less influx of fresh water from the tributary streams, due in 

 some measure to the low relief of the land, enabled marine faunas 

 to reach well toward the head of the gulf. These faunas indicate 

 subtropical bottom temperatures northward as far as Paducah, Ky. 

 The known floras are very scanty and unsatisfactory and in the 

 present state of our knowledge do not merit an extended discussion. 



Lower Eocene. 



The ^Midway Eocene was succeeded by a long interval during 

 which a great thickness of deposits was laid down which are col- 

 lectively known as the Wilcox Group. The character of these sedi- 

 ments and their faunas show that the gulf was somewhat restricted 

 and much shallower than in the preceding stage, with true marine 

 conditions prevalent only in its lower portion. The shores were 

 low and relatively flat. They were flanked by current- or wave-built 

 bars and separated from the mainland by shallow inlets or lagoons. 

 The lower courses of the streams were transformed into shallow 

 estuaries or broad swamps through which the smaller streams 

 meandered. The accompanying sketch map ( Fig. i ) shows the rela- 

 tion of land to water at this time. The shore line along which the 

 strand flora migrated is approximately indicated, and some of the 

 localities where fossil plants have been discovered in the littoral 

 deposits of this age are indicated by stars, while the general move- 

 ment of the warm ocean currents is indicated by arrows. A mag- 

 nificent flora is preserved at a large number of localities in the clay 

 .lenses which were formed in these estuaries and marginal lagoons. 

 This flora shows a mingling of tropical and subtropical types as far 

 northward as where the Ohio River now flows into the Mississippi. 

 It is of unparalleled richness and- preservation and will bear a more 

 extended analysis. 



Among the ferns it contains representatives of the genera Acro- 

 stichum, Pteris and Lygodinni, none of which appear to be common. 

 Both feather and fan palms are not uncommon. Conifers are rep- 

 resented by a single occurrence of a species of Arthrotaxis — a genus 

 which in the living flora is confined to the coastal swamps of Tas- 



