THE MISSISSIPPIAN PERIOD 



603 



within the limits of one period. It is for this reason primarily that 

 the Mississippian should be separated from the Pennsylvanian as 

 a distinct system. These physical changes were accompanied by 

 great changes in life, as will be seen. 



Fig. 427. Composite diagrammatic section, showing the unconformity 

 between the Mississippian and Pennsylvanian systems in Iowa. (Keyes, 

 la. Geol. Surv.) 



The Lower Carboniferous of Other Continents 1 

 Europe. The post-Devonian Paleozoic systems of Europe 

 resemble the corresponding systems of North America in some 

 ways, and are in contrast with them in others. The formations 

 in eastern and western Europe, as in eastern and western America,, 

 are notably unlike. In western Europe, two great series, or systems, 

 are included under the Carboniferous, namely, (1) the Lower Car- 

 boniferous, chiefly of marine origin, and (2) the Coal Measures or 

 Carboniferous proper, deposited partly in lagoons, marshes, and 

 lakes, and partly in the sea. These two systems correspond, in 

 a general way, to the Mississippian and Pennsylvanian, respec- 

 tively, of eastern North America. 



In southern Europe the Upper and Lower Carboniferous forma- 

 tions are like the Mississippian and Pennsylvanian of western 

 North America, in that they are chiefly marine. In eastern 

 Europe the Lower Carboniferous is partly marine, and partly non- 

 marine and coal-bearing, while the Upper Carboniferous is largely 

 marine. 



Though the rocks of the Lower Carboniferous series rest con- 



1 The term Lower Carboniferous is here used, instead of Mississippian, 

 because it is the term in common use in Europe. 



