i 9 i4.] SOUTHEASTERN NORTH AMERICA. . 133 



of the Wilcox in the most southerly areas of their outcrop. This 

 interval of emergence of the embayment area was followed by an 

 equally long interval during which a great thickness of deposits was 

 laid down that are collectively known as the Wilcox group. The 

 character of these sediments and their faunas show that the Missis- 

 sippi gulf was somewhat restricted and much shallower than in the 

 preceding epoch, 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 main- 

 land 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 maximum area covered or underlain by, Wilcox deposits is 

 also indicated on the accompanying sketch map (Fig. i, B-B) which 

 shows approximately the shore line along which the vegetation 

 migrated. As has been already remarked the Wilcox deposits have 

 yielded one of the most extensive of known fossil floras, an assem- 

 blage of extinct species which sheds considerable light on the phys- 

 ical conditions of the marginal lands of Wilcox time. 



Before taking up in detail the evidence of the flora I wish to point 

 out certain general climatic conditions based on cosmic causes and de- 

 duced for the Wilcox from studies of recent climates. 



It is to be noted that the factors governing atmospheric circulation 

 are general and not local and the relatively slight changes in the rela- 

 tion of land to sea in Wilcox time as compared with the present are 

 entirely too small to have caused much modification of existing con- 

 ditions. Then as now there was a persistent area of high pressure 

 over the North Atlantic and a low over the continent. Consequently 

 the winds were prevailingly from the east. Cyclonic disturbances 

 like those that originate today in the Gulf of Mexico or those more 

 violent and widespread storms of the West Indian hurricane type 

 which today originate in the Caribbean Sea would traverse at least a 

 part of the Mississippi embayment. So large an area of shallow 

 more or less landlocked water would have a very appreciable effect 

 in raising total temperatures and in the prevention of widely sepa- 

 rated extremes. At the same time it would increase the rainfall and 

 increase the width of the marginal lands over which this augmented 



