THE CRETACEOUS PERIOD 



239 



margin of the Atlantic and Gulf Coastal Plain. The northernmost 

 exposures are on Martha's Vineyard. The occasional gaps shown 



Fig. 149 

 Map showing the surface distribution (areas of outcrops) of Upper Cretaceous 

 strata in North America. (Modified by W. J. M. after Willis, U. S. Geo- 

 logical Survey.) 



on the map are due to the fact that the Upper Cretaceous beds are 

 there concealed under later deposits. From the outcropping belts 

 oceanward or gulf ward, the Cretaceous strata dip gently under the 



