424 GEOLOGICAL SURVEY OF THE TERRITORIES. 



(I consider dicotyledonous species only) leaves of a coarse coriaceous 

 texture, mostly with entire borders. A character of the same kind is 

 recognized in the flora of the Lower Lignitic group, which, like the former, 

 has very few dicotyledonous leaves with serrate borders, a large propor- 

 tion of coriaceous leaves, and also species of Viburnum with borders of 

 leaves equally cut by short-pointed teeth turned outside, a same kind 

 of dentation exactly which is remarked in a few dentate species of the 

 Dakota group. In the European Cretaceous flora, as represented by 

 Credneria, JEttingJiausenia, «&c., of the Quadersandstein of Germany, 

 the leaves have a fades, which, though different in some points, could 

 be, however, compared with that of a few species of our Cretaceous ; 

 for example, Ettingliausenia ISternbergii, Stiehler, or Fhyllites repandus, 

 Sternb., (figured in vol. ii,Tab.xxv, of Fl. derVorwelt,) could be admitted 

 as an original type of tlie multiple forms of Sassafras of the Dakota 

 group. But when we look further and come to the floras of the lowest 

 Tertiary of Europe, that of the lower Sezane for example, which, by the 

 presence of Cretaceous and Tertiary types, seem to indicate a flora of 

 transition between these two formations, and is recognized as Lower 

 Eocene, we find characters pointing out, I think, to a multiple kind of 

 derivation. This Sezane flora has its dicotyledonous types repre- 

 sented by 21 genera, with 47 species, with more or less serrate or 

 doubly-serrate and dentate leaves, and 11 genera, represented by 20 

 species, with entire-bordered leaves; therefore, a large predominance 

 of leaves marked by a character mostly absent from the Dakota group and 

 Lower Lignitic American floras. -.Considering this Eocene flora of France 

 only, with its species of Betula, 2 ; Alnus, 3; Ulmus, 2 ; Populus, 1 ; Salix, 

 3; Aralia,6; Greviopsis,5', Juglandites,4:; Celastrites,4; Bltamnus,!; &c., all, 

 even Salix, Juglaoidites, Rhamnus, with serrate leaves, it would be rational 

 to suppose that the original types of the dicotyledonous flora did repre- 

 sent essentially serrate leaves; while we had reason to admit a contrary 

 conclusion from the charactersof our Cretaceous and Lignitic floras, whose 

 types, even from the same genera, Juglans, Salix, Populus, are represented 

 by entire-leaved species. Also, in the dentate leaves of the North Amer- 

 ican Cretaceous aud Eocene, the type is distinct. With very few excep- 

 tions, these have the peculiar dentation remarked in the description of 

 Greviopsis Haydenii of Nebraska, and of Viburnun marginatum of Black 

 Butte. I have compared this last species to V. giganteum of Sezane, but 

 only for the size of the leaves and the character of the nervation, not for 

 the division of the borders, as seen above; for the Sezane species has 

 long, turned-upward teeth, some of them doubly dentate, a character in 

 accordance with most of the other kind of leaves of this European group. 

 How to account for discrepancies of this kind 1 Is the Sezane flora rep- 

 resentative of a formation absent from the American geology, or not yet 

 recognized in it ; of a land-formation which, under different climatic in- 

 fluences, could have harbored the same types as the Sezane ones, intro- 

 duced by some kind of agency 1 This is evidenth^ not the case, as the 

 series of the Cretaceous strata from the Dakota group to the Lignitic is 

 uninterrupted, and especially as both successive floras are related by 

 a general character far different from that of the conteraperaneous floras 

 of Europe and of those of intermediate epochs. Now, admitting that the 

 succession of generic tyiDes indicates continuous development or multipli- 

 cation of forms and characters in ascending from the lowest strata of the 

 geological formations, shall we say that a single form or type or species 

 has been at different times the first and only representative of each group, 

 though wide and multiple in its representatives it may be now ? Or, con- 

 sidering merely the dicotyledonous plants, which make their first appear- 



