Handbook of Paleontology 421 



ters encroaching upon the land formed the vast brackish- 

 water swamps in which thick coal beds were laid down. 

 Coal beds also accumulated in fresh water above but near 

 sea level. At the same time marine conditions prevailed 

 in the west and southwest with the deposition of lime- 

 stones and shales. The thickest Pennsylvanian deposits oc- 

 cur in the Ouachita mountains in Arkansas and Okla- 

 homa and in Alabama, where there is a maximum thick- 

 ness of 9000 feet, mostly coarse clastic material. In the 

 Maritime Provinces of Canada continental deposits to a 

 thickness of 10,000 to 13,000 feet represent this period. 

 In western United States in Oklahoma, Texas and the 

 southern part of the Great Plains country red beds and 

 gypsum and potash deposits appear in the higher series 

 of rocks, indicating an arid climate and the contraction 

 of seas toward the close of the Pennsylvanian or even in 

 Permian time. The close of the Pennsylvanian is marked 

 by a general retreat of the seas which continued into the 

 Permian. The late Mississippian and the Pennsylvanian 

 were times of crustal movement. High mountains came 

 into being in eastern Canada and the southern Appala- 

 chian area at the close of the former period and these 

 risings continued in the Pennsylvanian. The ancestral 

 Southern Rockies also came into being. Beds of iron 

 ore, but none of commercial value, are associated with the 

 coal of the Pennsylvanian and also oil and gas abound in 

 certain areas, as Oklahoma. 



In North America the Permian is a continuation of the 

 Pennsylvanian and its importance consists in that it is a 

 transition period between the Paleozoic and the Mesozoic 

 eras. Deposits of this age (Dunkard group) are repre- 

 sented in the east in southwest Pennsylvania and along 

 the Ohio river in Ohio and West Virginia by sandstones, 



