MESOZOIC TIME CRETACEOUS. 



813 



of greatest submergence in the course of the Cretaceous period. The vertical 

 lining indicates the parts that w^e submerged during the Lower Cretaceous ; 

 the horizontal lining, those that; were submerged during the Upper Creta- 

 ceous ; and the cross-lining, the ^reas under water through the whole period. 

 The map is too small for an indication separately of the fresh-water Creta- 

 ceous areas. f^ 



1349. 



North America in the Cretaceous period. 



The positions of the areas of Cretaceous rock-making, as illustrated for 

 the most part on the map, are the following : — 



1. The Atlantic border. 



2. The Gulf border to the Mississippi River. 



3. The Western Gulf border, or the area of Texas and Mexico. 



4. The Western Interior Continental Sea, including the summit region 

 of the Rocky Mountains, and extending south through New Mexico and 

 western Texas into Mexico. 



5. The Pacific border. 



Besides these there are the independent areas of Arctic lands. 



The submergence reached its maximum during the earlier half of the 

 Tipper Cretaceous. During the progress of Lower Cretaceous time, the great 

 Western Interior region was, for the most part, at or near the water level ; for 

 the outcropping beds are fresh-water or marsh-made formations. Only in 

 its southern part from Kansas over Texas, part of Kew Mexico and Mexico, 

 are they marine. At the same time the Atlantic border and the northern 

 Gulf border had their fresh-water formations. But after the Upper Cretar 



