154 Correlation of the Potomac Formations 



7. Similarity or diversity of contemporaneous physical conditions as 

 reflected by the character of sedimentation and the biota (ecological 

 grouping) . 



8. Stratigraphic continuity, similarity or diversity of the stratigraphic 

 succession. 



One of the first questions to be considered is the relation which the 



floras of the different Potomac formations bear to one another. The 



Patuxent flora, comprising about 100 species, contains the following 



forms, about two score in number, which have not been detected in the 



Arundel or Patapsco floras: 



SchizcBopsis americana 



Ruffordia Goepperti 



Acrostichopteris cyclopteroides 



Acrostiehopteris parvifoUa 



Dryopterites macrocarpa 



Dryopterites cystopteroides 



Dryopterites dentata 



Aspleniopteris pinnatifida 



Aspleniopteris adiantifoUa 



Onychiopsis brevifolia 



Sagenopteris latifolia 



Sagenopteris virginiensis 



Tceniopteris auriculata 



Tceniopteris nervosa 



Thinnfeldia rotundilo'ba 



Cycadeoidea (probably all nine species) 



Ctenopteris longifolia 



Ctenopsis latifolia 



Zamiopsis petiolata 



.Zamiopsis laciniata 



Zamites crassinervis 



Podozamites incequilateralis 



Podozamites distantinervis 



Baiera foliosa 



Cephalotaxopsis magnifolia 



Cephalotaxopsis brevifolia 



Cupressinoxylon Wardi 



Cupressinoxylon McGeei 



Laricopsis angustifolia 



Sequoia rigida 



Sequoia delicatula 



ProtewpTiyllum reniforme 



ProtecepTiyllum ovatum 



