162 Correlation op the Potomac Formations 



geologically, facts due in a considerable measure to their resistance of 

 maceration. The same statement would apply to the very meagre flora 

 described by ISTathorst from Mexico. 



The Lakota Flora oe the Black Hills 



The Lakota flora contains numerous silicified trunks of Cycadeoidea 

 similar in their external features and internal organization to those of 

 the Potomac, some of which may prove to be specifically identical when 

 their anatomy shall have been studied. In addition, at least 12 species 

 are common to the Potomac and the Lakota. These include 8 ferns, 

 1 equisetum, and 3 taxoid conifers, all of which are found in the Pa- 

 tuxent, 8 occur in the Arundel, and 10 occur in the Patapsco. None 

 of the modern types of the Patapsco are present, and the flora is certainly 

 pre-Albian in age. It is not as old as the basal Patuxent, and may be 

 considered to represent the upper pai-t of the Barremian and the lower 

 part of the Aptian of Europe. 



* The Fuson Flora oe the Black Hills 



The Fuson flora is a limited one, embracing only 26 identified forms, 

 of which 3 or 4 survive from the Lakota flora. At least 11 of the species 

 are more or less positively identified with species described originally 

 from the Potomac. Six of these range from the Patuxent through the 

 Patapsco. C ephalotaxopsis magnifolia is confined to the Patuxent, 

 while on the other hand, Sapindus variabilis is one of the type fossils of 

 the Patapsco, and far outweighs the former in any determination of age. 

 There are fragmentary remains of other dicotyledons in this flora, and 

 also a species of Geinitzia, a coniferous genus more especially character- 

 istic of Upper Cretaceous horizons. The Fuson therefore is considered 

 more or less synchronous with the Patapsco formation, and Albian in 

 age. 



The Kootanie Flora 



The Kootanie flora of Montana and British Columbia is an extensive 

 one, consisting of 86 nominal species, of which at least 20 are present in 



