Maryland Geological Survey 161 



which survive in both the Patapsco flora and that of the Albian of 

 Portugal. 



On the basis of this close similarity between these two floras on op- 

 posite sides of the Atlantic, and the fact that both mark the first abund- 

 ant appearance of Dicotyledonse, and the further fact that the Patapsco 

 formation, is overlain unconformably by the Pari tan formation, carry- 

 ing an abundant and unmistakably Cenomanian flora,* th'i Patapsco 

 formation is considered of Albian age. The unconformity which sepa- 

 rates the Patapsco formation from the underlying Potomac beds is 

 believed to represent all or nearly all of the time interval represented 

 by the Aptian stage of European geology. 



Having established with a considerable degree of certainty the Euro- 

 pean equivalents of the Potomac formations, a comparison may be insti- 

 tuted between the flora of the Potomac and that of other Korth American 

 Lower Cretaceous deposits. 



The Trinity Flora 0¥ Texas 



The Trinity flora is small and poorly preserved and is represented by 

 fragmentary remains of 25 species. 



Several of these occur in the Potomac. Of these Brachyphyllum par- 

 ceramosum, Cycadeospermum rotundatum, and Dioonites Buchianus do 

 not range above the Arundel, and while three or four species are common 

 to the Trinity and Patapsco floras, these all extend back to the Patuxent. 

 Since there are no characteristic Patapsco species in the Trinity it is 

 conclusively pre-Albian in age. As has previously been mentioned, 

 French paleontologists, upon the evidence of the invertebrate fossils, 

 consider the Trinity to be of Aptian age. The flora is not extensive 

 enough for direct comparison with the relatively scant floras of the 

 European Aptian, and while the writer would be inclined to consider 

 the Trinity as somewhat older than this, the contained flora cannot be 

 said to furnish reliable evidence contrary to such an assumption, since 

 most of the Trinity plants are widespread types, both geographically and 



' Berry, Journ. of Geol., vol. xviii, 1910, pp. 252-258. 



