CRETACEOUS PERIOD. 



489 



body is undergoing chemical change or decomposition, explains 

 the frequent occurrence of fossils within flints, and the silicifica- 

 tion of shells. 



2. American Geography. — The Cretaceous beds of New Jersey 

 and of the rest of the border region of the continent, east and south, 

 show in their structure and position, and in the character of their 

 fossils, that they were formed either along a sea-coast or in off- 

 shore shallow waters. Farther west, the limestones of Texas indi- 

 cate a clearer sea ; while the soft sandy and clayey formations to 

 the north are evidence that the same sea spread northward, but 

 mostly of diminished depth. 



The outline of the formation over the land points out approxi- 

 mately the outline of the sea in the Cretaceous period, and the 

 general form of the dry land. This is presented to view in the 

 accompanying map, in which the white part is the dry land of the 



Fig. 792 A. 



North America in the Cretaceous period^ MO, Upper Missouri region. 



continent, and the shaded the Cretaceous area, and therefore the 

 submerged portion. 



