CHAPTER IX. 



THE MISSISSIPPIAN (EARLY CARBONIFEROUS) PERIOD. 



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

 Paleozoic era was formerly regarded as a single period. Since the 

 formations of this period included many important coal-beds, the name 

 Carboniferous was assigned to it. During the course of the Carbon- 

 iferous period, according to the old definition, the following general 

 sequence of events seems to have taken place: 



(1) Early in the period there was an expansion of the interior 

 epicontinental sea, especially to the westward, decreasing, correspond- 

 ingly, the area of the land (Fig. 228). The deposits made in the sea 

 during this stage not only overlap the Devonian beds at many points, 

 but rest on strata older than the Devonian. The early Carboniferous 

 beds probably underlie the Great Plains, where the Devonian system 

 is believed to be absent, thus pointing to wide-spread submergence 

 in this direction. This interval of sea-transgression constitutes the 

 first major division of the Carboniferous period, as generally denned, 

 and has been variously known as the Subcarboniferous, Lower Carbon- 

 iferous, and Mississippian. It was brought to a close by wide- 

 spread emergence of the area where sedimentation had been in 

 progress. 



(2) During the next division of the period, as the term Carbonifer- 

 ous has been used generally, the sea was at first absent from much of 

 the area between the Appalachian mountains on the east and the 

 one-hundredth meridian on the west. This epoch of emergence seems 

 to have been followed by a brief epoch of submergence, and this by a 

 long interval during which the area of the eastern interior maintained 

 a halting attitude, being now slightly above the sea-level and now 

 slightly below it. This period of oscillation constitutes the second 



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