622 



GEOLOGY 



Fig, 435. Map showing the areas where the Pennsylvania!! system :i]>p<:ns 

 at the surface in North America. The map also shows, as in preceding 

 similar cases, the areas where the Pennsylvania system is thought to 

 exist though buried (lined areas); the areas where it is thought onn- to 

 have existed, but to have been removed by erosion (dotted); and by impli- 

 cation the relations of land and sea during the Pennsylvania!! period. 



