156 Correlation of the Potomac Formations 



of the Kootanie was approximately the same age or slightly older than the 

 base of the Patuxent. When the faunas are considered it develops that 

 the Morrison fauna, which is considered by many paleontologists to be of 

 Jurassic age, is found conformably beneath the beds containing the 

 Kootanie flora, which is of unquestioned Lower Cretaceous age. Along 

 the Atlantic seaboard this is reversed, and the bulk of the flora corre- 

 sponding to that of the Kootanie underlies beds containing a large repre- 

 sentation of the Morrison fauna, and which also has been considered to 

 be of Jurassic age by Marsh and others. 



The Patapsco flora, on the other hand, is decidedly different from the 

 flora of the underlying Arundel formation, and this difference is not so 

 much an extinction of earlier forms, although the extinctions have been 

 considerable, as it is an introduction of higher forms of a decidedly 

 Neocretaceous facies. 



The following older Cretaceous species, sixty-one in number, appear 

 to have become extinct before the dawn of the Patapsco. These include 

 17 ferns, 24 cycadophytes, 1 member of the ginkgoales, 2 taxaceous forms, 

 10 conifers, and all of the supposed primitive angiosperms, 7 in number : 



8chizcBopsis americana 

 Ruffordia Gcepperti 

 Acrostichopteris cyclopteroides 

 Acrostichopteris parvifoUa 

 Dryopterites macrocarpa 

 Dryopterites cystopteroides 

 Dryopterites dentata 

 Aspleniopteris pinnatifida 

 ■Aspleniopteris adiantifoUa 

 Cladophlebis Albertsii 

 Onychiopsis brevifolia 

 Sagenopteris latifoUa 

 Sagenopteris virginiensis 

 Twniopteris auriculata 

 Tceniopteris nervosa 

 TMnnfeldia rotundiloba 

 Thinnfeldia marylandica 

 Cycadeoidea (probably all nine species) 

 Cycadeospermum marylandicum 

 Cycadeospermum acutum 

 Cycadeospermum rotundatum 

 Cycadeospermum spatulatum 



