CHAPTER XX 

 THE MISSISSIPPIAN (EARLY CARBONIFEROUS) PERIOD 



FORMATIONS AND PHYSICAL HISTORY 



The time from the close of the Devonian period to the end of 

 the Paleozoic era was formerly regarded as the Carboniferous period. 

 But this interval is now commonly divided into two or three divis- 

 ions, each of which is given the rank of a period. If three divisions 

 are made (as here), the first is the Mississippian period, also known 

 as the Subcarboniferous, or Lower Carboniferous. It represents a 

 time of wide-spread submergence of the North American continent, 

 and was brought to a close by wide-spread emergence of the area 

 where marine sedimentation had been in progress. The second, 

 the Pennsylvanian period, (also known as the Carboniferous, Coal 

 Measures, and Upper Carboniferous), represents a time when the 

 area between the Appalachian Mountains on the east and the 100th 

 meridian on the west maintained a halting attitude, being now 

 slightly above sea-level and now slightly below it. West of the 

 Great Plains, submergence was rather general, as during the 

 preceding period. The third division of the old Carboniferous 

 period is the Permian, a time of notable crustal deformation, 

 general aridity, and, during part of the period at least, low tem- 

 perature. 



The Mississippian was a period of widespread submergence, a 

 submergence which began in the late Devonian; but its close was 

 marked by the emergence of large portions of the continent. In 

 keeping with this definition of the period, the earlier beds, deposited 

 while the advance of the sea was in progress, are less wide-spread 

 than those of later stages, when submergence had become more 

 general. 



596 



