Maryland Geological Survey 165 



probably represent dicotyledons, the botanical affinities of which are 

 entirely conjectural. Since there are no distinctively Patapsco types in 

 this formation it is believed to correspond with all of the Aptian stage 

 of European geology, possibly representing, in addition, the later Bar- 

 remian and the early Albian. 



General Considerations 



Additional Lower Cretaceous floras from South America, Europe, Asia, 

 and Africa have been discussed in the preceding chapter, and their ar- 

 rangement has given ample expression of the writer's opinion of their 

 relative ages as derived from a study of these floras. It does not seem 

 worth while to attempt a detailed analysis of these floras at the present 

 time, since lists of species and citations of authorities have already been 

 given, while the accompanying tables of distribution amply illustrate their 

 points of contact with the floras from the different formations of the 

 Potomac Group. 



While the geological range of a large number of these species is not 

 known with precision, the data at hand are suflicient to justify the table of 

 correlations given on page 172, especially as there is a considerable body 

 of stratigraphical and paleo zoological evidence in confirmation of that 

 which is paleobotanical. 



The liability to error in attempting correlations between remote areas 

 is fully appreciated, and it would be unreasonable to suppose that the 

 exact limits of a number of these floras will not be shifted back and 

 forth as new or better evidence is discovered. Nevertheless the relative 

 position of the main body of the respective floras in Lower Cretaceous 

 chronology is believed to rest upon a fairly secure foundation. 



