238 



HISTORICAL GEOLOGY 



Upper Cretaceous. As seen on map Fig. 149, the rocks of 

 Upper Cretaceous age are widely exposed at the surface — much 



Fig. 148 

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

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

 logical Survey.) 



more so than those of Lower Cretaceous age. In the eastern and 

 southern United States, Upper Cretaceous strata outcrop as com- 

 paratively long, narrow belts at or near the western and northern 



