PALEOGEOGRAPHIC MAPS 



BAILEY WILLIS 

 U. S. Geological Survey 



7. PENNSYLVANIAN' 



The passage from Mississippian to Pennsylvanian was charac- 

 terized by that emergence of lands, which is indicated on the map by 

 the districts assigned to continental deposits and temporary lands. 

 In the eastern United States the tendency toward emergence was 

 progressive though interrupted. In the central west the emergence 

 was but temporary and the transient land area was submerged under 

 the Pennsylvanian sea. In contrast with the Mississippian, the Penn- 

 sylvanian continent probably extended far to the west — north of the 

 fortieth parallel. As is shown by White there was land connection 

 with England and Europe, probably around the North Atlantic. 



The southeastern portion of the continent appears to have been 

 embraced by branches of the equatorial Atlantic current. The 

 northwestern part was washed by currents from the Arctic and north 

 Pacific. The period was one during which climatic differences devel- 

 oped, and the situation of North America favored that development. 

 The accumulation of coal in the southeastern portion in contrast 

 to red sediments in the southwestern part may thus be explained as 

 an effect of climate, in the one district favorable, in the other unfavor- 

 able to vegetation. Red beds are to some extent interbedded with 

 coal measures, as glacial deposits of the Pleistocene are with inter- 

 glacial, and it is probable that the relations may be interpreted as 

 evidence of climatic fluctuations. 



1 Prepared in conference with Dr. G. H. Girty. 



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