442 



PENNSYLVANIAN PERIOD 



Fig. 383. Map showing the areas where the Pennsylvanian system appears at 

 the surface in J^orth America. The map also shows, as in preceding similar cases, 

 the areas where the Pennsylvanian system is thought to exist though buried (lined 

 areas) ; the areas where it is thought once to have existed, but to have been removed 

 by erosion (dotted); and by implication the relations of land and sea during the 

 Pennsylvanian period. 





