THE MISSISSIPPIAN PERIOD. 499 



Formations and Physical History. 



The transition from the Devonian period to the Mississippian seems 

 to have been accomplished without notable deformative movement, so 

 far as the larger part of North America is concerned. This is shown 

 by the fact that the earlier formations of the Mississippian period 

 covered most of the area where Devonian sedimentation had been 

 in progress, and that the formations of the later system are, in general, 

 conformable on those of the earlier. These relations hold for both 

 the eastern and western parts of the continent. On the other hand, 

 the Mississippian strata are more wide-spread than the Devonian, 

 indicating that the interior sea of the Mississippian period spread some- 

 what more widely over the continent than that of the late Devonian 

 period. The Catskill region, except perhaps its western part, appears 

 to have ceased to be an area of sedimentation (compare Figs. 196 and 

 228), and in the eastern part of the continent, especially in New Eng- 

 land and the Acadian region to the north, sedimentation was inter- 

 rupted, for there the Carboniferous beds often overlie the upturned 

 and eroded Devonian strata unconformably. 



The Mississippian period may be looked upon as beginning with 

 the beginning of the continental submergence which followed the 

 Devonian period, and as ending with the emergence of considerable 

 areas of the continent, and a corresponding restriction of the epi- 

 continental sea (Fig. 229). From this definition of the period, it 

 follows that the earlier beds, deposited while the advance of the sea 

 was in progress, are more restricted in their distribution than those 

 of a somewhat later stage, when the continent was more generally 

 submerged beneath the epicontinental sea. 



Throughout the period, the interior sea seems to have been bounded 

 on the north, the east, and the south by land, though there were prob- 

 ably connections with the ocean in these directions. To the west 

 it opened broadly, though less is known concerning its extension 

 in that direction. In the interior sea of the east, and in the more 

 open sea of the west, there were the conditions for varied sedi- 

 mentation. 



