832 



HISTORICAL GEOLOGY. 



hensive features, indicative of early forms. The Cycad genns, Dioonites 

 (Fig. 1350), occurs in the ISTeocomian of Europe (at Wernsdorf), and is very 

 common in the Potomac beds. Fontaine says, in his conclusion, that the 

 flora ranges from the Wealden through the Neocomian, and includes some 

 later (Cenomanian) forms. All, or nearly all, the species are absent from 

 the later Cretaceous beds of New Jersey. 



1350-1353. 



Plants of the Potomac GrKOtrp. — Cycad. — Fig. 1850, portion of a frond of Dioonites Buchianus. Angio- 

 SPBKMS. — Fig-. 1351, Ficus Virginiensis ; 1852, ProtsBiphyllum reniforme. Fern. — Fig. 1853, Sphenopteris 

 Mantelli. All from Fontaine. 



The plants of the Trinity beds of Texas are to a large extent identical, 

 according to Fontaine, with those of the lower Potomac beds (1893). They 

 include Cycad stumps named Cycadeoidea munita by Cragin. Cycadeoidea 

 Jenneyana of L. F. Ward occurs in the form of stumps at the Black Hills, on 



