Maryland Geological Survey 159 



though none of the specific types except Podozamites KnowUoni and 

 CelastropJiyllum Brittonianum survive in the succeeding Earitan flora. 



It seems obvious that this striking modernization of the flora which is 

 first seen in the Patapsco, corroborated by tbe well-marked erosional 

 unconformity between the Arundel and Patapsco formations in regions 

 where the former intervenes between the Patuxent and Patapsco, indicates 

 an interval of long duration, an interval during which the angiosperms, 

 which so greatly outnumber any other class of plants in Upper Cretaceous 

 and more recent floras, were evolved. 



We are forced to the conclusion that the Patuxent-Arundel floras are 

 essentially a unit of early Cretaceous age whose affinities all lie with the 

 floras which preceded them, while the Patapsco flora, widely removed in 

 time from the Patuxent- Arnndel, heralds the approaching dominance 

 of a new and more highly organized type of vegetation which was destined 

 to so largely replace the strictly Mesozoic plant types early in Upper 

 Cretaceous time. 



Turning now to a comparison of the Potomac floras with floras outside 

 of the Potomac province we may endeavor to fix their place in the Lower 

 Cretaceous time scale of the world. 



The European- Floras 



It is obvious from a penisal of the discussion in the chapter devoted 

 to the Lower Cretaceous floras of the world that no arguments are neces- 

 sary to prove that the Patuxent-Arundel flora is post-Jurassic in age, a 

 conclusion amply sustained by Professor Lull's discussion of the reptilian 

 remains from the Arundel beds. 



The Patuxent-Arundel flora contains but 3 species which have been 

 recorded from the Portlandian, i. e., CladophleUs Browniana and Sequoia 

 EeichenbacM, and one additional older Mesozoic species, Podozamites 

 Janceolatus, which, with the Sequoia, is of no significance since both 

 continue through the Upper Cretaceous, and both may be composite 

 11 



