474 



MESOZOIC EKA— AGE OF REPTILES. 



Lowee Tertiary. 



AMERICAN. 



EUROPEAN. 



Western Plains. Atlantic Border. 



Wahsatch and Puerco beds. 



Eo-lignitic. 



Plastic clay, Thanet sands. ; 



Transition. 



Laramie. 



Wanting. 



Wanting. 



Cretaceous. 



Upper 1 Foxhi11 S rou P- 

 1 1 ( Colorado group. 



Middle.Dakota group. 



Lower. Comanche group. 



N. J., Penn., and 

 Miss. 



Wanting. 



Wanting. 



j White chalk. 

 1 Gray chalk. 

 S Upper Greensand 

 ( Gault. 

 Neocomian. 



Transition. 



Trinity beds. 

 Eaptanodon beds. 



Potomac formation. 



Wealden. 



Upper Jurassic. 



Wanting. 



Purbeck. 



Life-System : Plants. 



Leaf-impressions are very abundant in the American Cretaceous, 

 and the most cursory examination reveals at once a type of plants not 

 seen in any lower rocks, viz., Angiosperms, both Dicot}'ls and Palms. 

 We have said that the Sierra revolution at the end of the Jura-Trias 

 produced important changes in America. A great break in the record 

 occurs at this time in the region (the Plains) where these plants were 

 found. When the record commences again in the Dakota epoch we 

 observe a very great difference in the subject-matter. The whole as- 

 pect of field and forest must have been different and much more mod- 



Fig. 763. 



Fig. 764. 



Fig. 765. 



Figs. 763-765.— Cretaceous Plants, Dakota Grout (after Lesquerenx): 763. Liquidambar in- 

 tegrifolium. 764. Laurus Nebrascensis. 765. Quercus primordialis. All reduced. 



