296 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



sumiug, and notwithstanding that Ahietites, which I consider as a Cre- 

 taceous type, your first group seems indeed to be legitimately Eocene, 

 by its Ferns, its Palms, its coriaceous and prototypical Poplars, its 

 Cinnamomum^ and its Viburnum, as related to the S6zanne flora, and by 

 one of its Palms to the Upper Eocene of Angers. If one would suppose 

 this flora more recent than the Eocene, he would have to admit such a 

 dissemblance between Europe and America that every comparison by 

 the floras between the geological stages of both continents should ap- 

 pear an impossibility." The assimilation of American species with a 

 number of Miocene species published in Europe is considered by Saporta 

 as doubtful and not quite conclusive ; and he remarks, also, that, though 

 his opinion on the age of the Lower Lignitic group is given according 

 to present impression, the great geographical distance renders the 

 affinities between compared localities very diiflcult to fix with precision, 

 even in supposing them contemporaneous. 



These quotations must be excused by reason of the importance given 

 now to the question of the age of the Lignitic, which, controverted in 

 various ways, demands light, and has to be considered in every possible 

 jjoint of view. The problem is not yet solved. Eequested, as I am, to 

 contribute a share in the discussion, by closely adhering to paleontologi- 

 cal evidence, and exposing it as far as it is given by fossil plants, I had 

 to enter into details in order to show its weight. And no better oppor- 

 tunity could be afforded for this purpose than a review of the group of 

 plants obtained from Point of Eocks by Dr. Hayden. 



From the following descriptions it will be remarked that some of the 

 specimens have been found and communicated to the survey by Mr. 

 William Cleburn, of Omaha, a zealous exj)lorer and student of the vege- 

 table paleontology of the Western Territories. 



Description of species of fossil plants from Point of BocTcs. 



1. Fucus LiGNiTUM, sp. nov. 



Frond flattened, irregularly dichotomous ; branches diverging ob- 

 liquely ; branchlets short, terminal, linear- divaricate, tufted, forking at 

 the point. 



The fragment figured is the only one of this kind in the specimens. It 

 represents a species allied to Sphcerococcus crispiformis, Sternb., as de- 

 scribed in Heer's Flor. Tert. Helv. (p. 23, PI. IV, fig. 1), and still more, 

 perhaps, to the living Fucus canaUculatus, Agh., very common along the 

 coasts of the Baltic Sea, and also discoverd in numerous specimens in 

 the Tertiary of Spitzbergen. The base of the lowest branches is four 

 millimeters broad, but the size of the branchlets diminishes nearly one- 

 half at each dichotomous division. The terminal branchlets are only 

 half a millimeter broad, fasciculate-dichotomons, short, split, or furcate 

 at the point, and divaricate. The substance appears thin, membrana- 

 ceous, and yellowish. 



Habitat. — Point of Eocks, Dr. F. V. Hayden. 



2. Salvinia attenuata, sp. nov. 



Leaves small, one centimeter or less in diameter, opposite, joined at 

 the narrowed, slightly-pediceled base, round or broadly oval, indis- 

 tinctly reticulate by vertical and parallel rows of quadrate, large cells, 

 marked in the middle by black spots, formed by very small, close cells, 

 or pores, without any trace of a middle nerve. 



This fine species is related by its reticulation and its size to Salvinia 

 Mildeana, Heer (Bait. Flor., p. 17, PI. Ill, figs. 1 and 2), differing from 



