GENERAL CONCLUSIONS. 43 
describes thirty-two species, and quotes, in the comparative examination, 
most of those known in Europe from the same formation. Not one of them, 
however, offers a close affinity to the plants of the Chalk Bluffs. This 
difference is explainable by the likeness of the characters of the Plio- 
cene species to those of the present time,—a relation which reduces the 
affinities to local or geographical limits, as they are now. The circum- 
scriptions are wider, or the geographical areas less distinctly fixed in 
older geological divisions, and thus the flora of the Chalk Bluffs has 
some Miocene species identifiable in Europe, but none of its Pliocene 
as yet. . 
On another side, in coming nearer to the present period the vegetable 
forms become more and more similar to those of our time, some being 
apparently identical. But it is very difficult to make out positive iden- 
tity from the characters. of leaves only. The identity is probable, evi- 
dent to the eyes of the observer; but it cannot be proved. For species 
of this kind a derivative appellation, indicating supposed identity, like 
pseudo or the terminative ies, seems more appropriate. The authors of 
the “Flora of Maximieux” append to the specific name the epithet phocene, 
and thus have Populus alba (plocenica), etc. 
The Miocene relation of the flora of the Chalk Bluffs is indicated by 
a few identical species: Fagus Antipofi, Heer, described from the Miocene 
of Alaska, of France, and of Arctic Russia; Populus Zaddach, Heer, pre- 
dominant in the Upper Miocene of the Baltic, and found also in the same 
formation of Alaska, Greenland, and Spitzbergen; Ficus tilicfolia, Al. Br., 
present in the whole Miocene of Europe as far north as (ningen, and 
in the North American from the Lower Lignitic measures, which I con- 
sider as Lower Eocene, through the different stages of the Tertiary; Arala 
Zaddachi ? Weer, whose identification is as certain as it can be made in 
the comparison of our specimens with the mere fragment which repre- 
sents this species from the Baltic Miocene. Besides this, we find a marked 
affinity between Quercus elenoides and Q. elena, Ung. a common Miocene 
species of Europe; Salix elliptica, related to S. varians, Goepp.; Lveus sor- 
dida, closely allied to, if not identical with, F. Granlandica, Heer, of Green- 
land; F. microphylla, which seems a mere diminutive form of /. planicostata, 
a common species of the Lower Lignitic of the Rocky Mountains; Aralka 
Whitneyi, related to A. affm’s of the group of Evanston, Middle or Upper 
Eocene; Acer aguidentatum, related to Acer vitifoliun of (Eningen in a 
