MESOZOIC ERA.A&E OF REPTILES. 361 



As we might expect, we find Cretaceous types lingering 

 and Tertiary types coming in, and the two coexisting 

 side by side. The Cretaceous dinosaurs linger, but the 

 Tertiary plants are introduced. The paleo-zoologists are 

 disposed to ally it with the Cretaceous, and the paleo- 

 botanists with the Tertiary. It is really a transition be- 

 tween the two. 



Plants. Vegetation was luxuriant at this time. More 

 than three hundred species of dicotyls have been described 

 here. But, as the types are wholly Tertiary, we shall illus- 

 trate them under that head. 



Coal. The conditions seem to have been favorable, 

 not only for luxuriant vegetation, but for its preserva- 

 tion as coal, and nearly all the Cretaceous coal mentioned 

 on page 351 belong to this transition period, and have 

 therefore been often put in the Tertiary. Next to the 

 Coal-measures, this is the great coal-bearing period of 

 the United States. The largest fields are in the Plains 

 and Plateau region, viz. : 1. A large field, the Marshall 

 coal-field, in western Kansas, about 5,000 square miles. 



2. Another large field, in New Mexico, of equal size. 



3. A third large field, in Dakota, extending into British 

 America. 4. A large and valuable field, in the Plateau 

 region, on the Laramie Plains, stretching through Wyo- 

 ming to the borders of Utah. These altogether can not 

 be less than 50,000 square miles. On the Pacific slope 

 several coal-fields, probably of the same age, are found : 

 1. Mount Diablo and Corral Hollow field. 2. Seattle, 

 Carbon Hill, and Bellingham Bay field. 3. Nanaimo or 

 Wellington field on Vancouver's Island. Coal is also 

 found in Arizona and in southern California, but the age 

 is not known. 



All the later coals are often called lignites, but much 

 of it is an excellent coal, scarcely distinguishable from 

 carboniferous coal. We herewith present in tabulated 

 form all the principal coal-fields of the United States : 



