128 



Tilia, sEsculus; all the serrate Rosacea; Hcnnamelis, Fraxinus; the Urticinece, 

 Planera, Ulmus, Moras; and of the Amcntacece, the serrate Betula, Alnus, 

 Ostyra, Carpinus, Corylus, Carya, &c. 



This enumeration exposes the general fades of the leaves or of the flora 

 of the Dakota group, viz, integrity of the borders and coriaceous consistence 

 of the leaves. The borders, if not perfectly entire, are merely undulate or 

 obtusely lobed. There is only one exception to this in that peculiar short 

 denticulation with outside turned teeth, which is marked, exactly of the same 

 kind, in Greviopsis haydenii, Platanus newberrii, Protophyllum mudgei, and 

 the fragments described as Phyllites betulcefolius. This mode of division of 

 the borders of leaves is very rare in species of our present times, except, 

 perhaps, in some leaves of poplars. 1 One species only of the Dakota group, 

 Quercus prhnordialis, has its leaves with borders distantly serrate, or 

 marked by teeth turned upward. There is, also, in the flora of the Eocene 

 of the Rocky Mountains a marked preponderance of leaves with entire 

 borders. The serrate leaves appear in the Miocene with Acer, Alnus, Cory- 

 lus, and become predominant in the Pliocene of California, where Ulmus, 

 Planera, Celtis, and Carya abound, though these genera are not recognized 

 till now in the flora of the Pacific slope. 



But of the detailed correlation of the flora of the Dakota group with that 

 of the subsequent geological epochs of this continent, I will say nothing more 

 until the materials on baud are definitely described and figured for com- 

 parison. 



There is as yet little to say on the relation of the Dakota group flora 

 with that of any of the Cretaceous groups of Europe, especially on account of 

 deficiency of materials for comparison. Of the ferns, Gleicheinia kurriana, 

 represented in the Cretaceous of Kansas, is found also in that of Moletiu, of 

 Quedlinburg, and even of Belgium, if, as I believe it, Didymososaurus comp- 

 toniifolius is identical with it. Pecopteris nebrascensis, Heer, is closely related to 

 RaphaUia neuropteroid.es, and Todea (?) saportanea to Monheimia equisgranen'sis, 

 both of the same Belgian formation. In the cycadea3 (?) and conifers, Ptero- 

 phyllum haydenii has been compared to P. ernestince of the Quadersandsteinof 

 Blankenburg ; Sequoia reichenbachi is in the Upper Cretaceous of Greenland; 

 and Glyptostrobus gracillimus may be identical with Frenelites reichii of 



1 It is, however, remarkably predominant in the leaves of the Lower Eocene of Sezane, as also the 

 serrate divisions, as seen in the splendid work of Saporta on the Flore fossile of this formation. 



