THE MISSISSIPPIAN PERIOD 153 



Climate 



As for the earlier Paleozoic periods, the character and distri- 

 bution of Mississippian fossils pretty clearly prove absence of 

 climatic zones like those of today. A mild, uniform climate ap- 

 pears to have prevailed. Salt and gypsum beds more or less 

 associated with red beds point to arid climate in Michigan, 

 Montana, Nova Scotia, and Australia, but these were probably 

 local conditions. Evidence of glaciation toward the close of the 

 period has been reported from Oklahoma. 



Economic Products 



Much oil is obtained from Mississippian sandstones in western 

 Pennsylvania. West Virginia, Illinois, and Oklahoma. 



Some gas is obtained from the Chester sandstone of Illinois, 

 and some coal from the Pocono sandstone of West Virginia. 



Building stones of Mississippian age are considerably quarried, 

 especially the oolitic Bedford limestone of Indiana, which is per- 

 haps the most widely used limestone for building stone in the 

 United States. 



Vast quantities of salt are produced by pumping out and evap- 

 orating the natural brines from the Mississippian sandstones of 

 Michigan, and smaller quantities from the sandstones, or lime- 

 stones of Ohio, West Virginia, and Virginia. 



Certain important zinc ore deposits occur in the Lower Missis- 

 sippian limestones of Missouri and Kansas though the deposition 

 of the ore was post-Mississippian. 



Life of the Mississippian 



Plants. — In general the flora of the Mississippian may be 

 said to have been very much like that of the Devonian, though 

 the former showed greater diversity and various minor changes. 

 Because of the prevalence of marine waters during much of the 

 time, the records of land plants are perhaps not as full as those of 

 the preceding period. Fossil plants are most numerous in early 

 Mississippian rocks. 



The simplest plants, such as Thallophytes and Bryophytcs, 

 were present but their fossil forms are not known to be common. 



