CHAPTER XV. 

 The (Later) Cretaceous Period. 



The Later Cretaceous period (which will hereafter be called the 

 Cretaceous) may be said to have been ushered in, so far as North 

 America is concerned, by a notable encroachment of the sea on the 

 land. 



Within the land area of the North American continent, the Creta- 

 ceous occurs (1) along the Atlantic Coastal plain; (2) along the 

 corresponding plain of the Gulf, both east and west of the Mississippi ; 

 (3) over the region of the Great plains, probably stretching north contin- 

 uously from the Gulf of Mexico to the Arctic ocean; (4) at many 

 points in the Cordilleran mountains, and (5) over considerable areas 

 along the Pacific coast. In all these regions, the system is chiefly marine, 

 though not without extensive fresh- water or terrestrial deposits. It 

 thus appears that while the geographic distribution of the Cretaceous 

 system has much in common with that of the Comanchean, the 

 younger system is much more widespread (Fig. 388). 



The Atlantic border region. 1 — The Cretaceous beds of the Atlantic 

 coast come to the surface in a belt near the western margin of the 

 Coastal Plain, immediately east of the outcrop of the Lower Creta- 

 ceous system. The principal exposures are in New Jersey, Delaware, 

 Maryland, and Virginia. The lowest beds are not believed to repre- 

 sent the earliest beds of the system as developed elsewhere. The 

 Cretaceous beds have been but little disturbed, and still dip, as when 

 deposited, slightly to seaward. In that direction the beds pass 

 beneath later formations. 



The Cretaceous formations of the Coastal Plain are made up of 

 conformable (probably) beds of clay, sand, limestone, and greensand 



1 Besides the State Reports referred to under the Comanchean, see Clark, Bull. 

 Geol. Soc. of Am., Vol. 8, 1897, pp. 315-358, and Weller, Jour, of Geol., Vol. XIII. 

 p. 71. 



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