CHAPTER XXX 

 THE CRETACEOUS PERIOD 



The name Cretaceous is derived from the Latin word for chalk 

 (Crete), because in England, where the name was early used, the 

 thick masses of chalk are the most conspicuous members of the 

 system. 



In very marked contrast to the scanty development of the Jura, 

 the Cretaceous strata of North America are displayed on a vast 

 scale, and cover enormous areas of the continent, eloquent wit- 

 nesses of the great geographical changes in that long period. 

 Fresh-water, estuarine, and marine rocks are all well represented, 

 and, in consequence, our information regarding the life of North 

 America and its seas during Cretaceous times is incomparably 

 more complete than it is for the Triassic and Jurassic. 



The Cretaceous rocks of North America are of very different 

 character in the different parts of the continent, and require sepa- 

 rate classification. 



Distribution of Cretaceous Rocks 



American. — At the opening of the Cretaceous, the Atlantic 

 coast of North America appears to have been farther to the east- 

 ward than it is at present ; but just as had happened in the Triassic 

 period, a long, narrow depression was formed, running roughly 

 parallel with the coast, and in this depression one or more bodies 

 of water accumulated, in which, for a long period of time, sedi- 

 ments in the form of sands and clays were deposited. This 

 Potomac series, which is divisible into several stages, has , been 

 traced through the islands of Martha's Vineyard, Nantucket, 

 Block Island, Long Island, Staten Island, across New Jersey, and 



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