244 



derance of Palm remains indicates for this flora a climate different from 

 that of the Dakota group. In considering the numerous and thick coal- 

 beds of the Lignitic, it is evident that the atmosphere was, at this epoch, 

 charged with a high degree of humidity, which, tempering the climate 

 by diminishing the extremes of heat and cold, furnished the conditions 

 for a different kind of vegetation. Circumstances similar to those re- 

 marked at the Carboniferous period are reproduced in the Lignitic, where 

 also extensive flats, wide surfaces of land slowly emerging from the sea, 

 were for a long time under an atmosphere of fogs and vapors. The veg- 

 etation was then somewhat similar in its aspect to that of the swamps 

 now along the Gulf shores of the South; and thus, in comparing the flora 

 of the Dakota group to that of the Lower Lignitic, their general facies 

 indicates about the same difference of temperature as is marked at the 

 present time by the vegetation of Ohio as compared to that of Southern 

 Louisiana and Florida, where the Palm family is represented by Sabal 

 and Chamaerops. The relation of the flora of the Lower Lignitic with 

 that of our time is more distinctly marked by the Magnolias, which 

 closely resemble living species, at least as to their leaves. The Oaks are 

 more numerous also. Among them appear the first type of the group 

 of our Black and Red'Oaks, with deeply-lobed leaves, like those of Quer- 

 cus lyrata and Q. falcata. The Lignitic flora has, besides, species of 

 Gornus^ Yitis, Nelumhium^ Sapindus, Zizyphus, well characterized Juglans, 

 Glumacece like Arundo, Phragmites, Carex, and a considerable number of 

 large Ferns ; Woodwardia, Pteris, Lygodium, all genera represented now 

 in the North American flora, and not in that of the Dakota group. The 

 Maple {Acer) is not positively recognized in the Lower Lignitic. Betula 

 and Alnus are as indistinctly and sparingly represented as in the Cre- 

 taceous flora. About two hundred species have been already described 

 from the Lower Lignitic of the Rocky Mountains and of the Mississippi. 



Considering the distribution and the relation of the plants found at 

 different localities, the Tertiary formations of the Rocky Mountains 

 have been divided into four sections : 1st. The Lower Lignitic, whose flora 

 has been remarked upon, is referable to the Eocene •, 2d. The Evanston 

 group, considered as Upper Eocene or Lower Miocene ; 3d. The Carbon 

 group, or Middle Miocene; 4th. Green River group, or Upper Mio- 

 cene. 



The flora of the second group is represented as yet by about ninety 

 species, of which nearly one-third are identical with those of the lower 

 stage. It has a number of fruits, which have been considered as referable 

 to Palm ; but no leaves of Sabal or of other species of this family have 

 been found with them. Therefore, the presence of Palms in these beds is 

 still uncertain. The fossil plants of this section have, for the first time, 

 a number of species, with dentate and serrate leaves, of Salix, Betula^ 

 Alnus, and Acer. 



The general characters of the flora partake of both those of the first 

 and third group. lbs plants, however, should be more abundantly col- 

 lected and better known before its geological station is definitely fixed. 

 It may represent merely an upper member of the first group. The third 

 group is especially known by the fossil plants,which are found in abundance 

 in the shale overlying the Lignite beds of Carbon ; they represent a flora 

 mixed in its characters, and consequently of great interest. Its general 

 facies is positivel3^ Miocene ; for of the fifty-six species which represent it, 

 eighteen are identical with forms of the European Miocene, and thirteen 

 with those of the Arctic flora described from Alaska, Greenland, and 

 Spitzbergen. It has still, however, a few species that may be consid- 

 ered remnants of the Lower Lignitic, and are not present in the Arctic 



