WA.,1,.] VKGETATIOX OF THE LARAMIE AGE. 439 



lose their leaves by the action of frosts and that subtropical species, 

 like the palms, the figs, and the ciuiiaiuons, could subsist. In the second 

 place, it must be remembered that the Laramie period was a very pro- 

 longed one, and within it there was time for considerable alteration of 

 climate on this continent or even on the whole globe. But even ad- 

 mitting that this was too slight to be perceptible, the changes that took 

 place in the form of the continent and the distribution of land and 

 water on it during that time might have been sufficient to produce 

 marked effects and render the later floras of the Laramie age quite dif- 

 ferent from its earlier floras. 



The Fort Union beds, containing the genera Corylus, Sapindus, and 

 other forms of recent aspect not found in the Bitter Creek and Golden 

 deposits, are believed to be high up ini;he series; and I have myself 

 found and explored others within the general district included by that 

 group which 1 have proved stratigraphically to occupy a considerably 

 lower horizon, and in which these forms of recent aspect not only do 

 not occur, but some of the most characteristic Laramie types, such as 

 Trapa microphylla and Pistia corrugata, do occur, together with other 

 forms not previously known as Laramie. In tact, it is well known that 

 the Fort Union Laramie is everywhere thinner than the more southern 

 deposits, none of the sections making it over 3,000 feet in thickness. 

 The beds to which I refer rest immediately upon the typical Fox Hills, 

 ami therefore represent the lowest strata present in that section. I am 

 not yet prepared to speak upon the precise affinities of this lower Fort 

 Union flora, not having completed the elaboration of my material, but 

 I can say this much, that besides containing some of the more southern 

 Laramie forms, its general aspect indicates a much warmer climate than 

 that which prevailed at the time of the deposition of the Corylus and 

 Viburnum beds above. 



Fully conceding, as I do, that the geological age of the Laramie 

 group cannot, for the reasons stated, be proved by its flora alone, and 

 holding that even great similarity of flora would not be conclusive as 

 to synchronism of deposit, I have still thought it instructive, in view 

 of the warmth with which the Cretaceous and Tertiary theories for 

 the age of this group have been respectively advocated, to make some 

 general comparisons of its flora with those of the extreme upper Creta- 

 ceous and lower Tertiary of those parts of the world where the strati- 

 graphical position has been settled. In the several elaborate tables of 

 distribution of the species of the Laramie group which Mr. Lesque- 

 reux has drawn up and employed to demonstrate its Eocene age, it is 

 noticeable that he has seemed to ignore almost altogether the existence 

 of a large upper Cretaceous flora lying entirely above the Cenomanian 

 • and its American e.iuivalent, the Dakota group. In a paper which ap- 

 peared in the American Journal of Science for April, 1884, 1 succeeded 

 in getting together 2G0 species of Dicotyledons alone from this forma- 

 tion, which I designated as Senonian, and in a table published in the 



