338 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



ill lakes wliosc oiitliiics are in some localities still traceable, lias taken place 

 within tlie area of the upheaved country, or within the range of the mount- 

 ains. And though, therefore, they represent an epoch far distant from the 

 Eocene, the climatic circumstances may not have been as yet greatly modified; 

 for we find still, in the flora of the fourth group, a few species of Ficus, none, 

 however, of the Eocene type; of Sapindus, Acacia, Mimosifes, etc., or rep- 

 resentatives of genera which, at our time at least, demand for their life an 

 average temperature of a liigher degree than it could have been in the 

 uplands, if the atmosphere in the region of the plains had been already cooled. 

 It must be remarked, in regard to this question, that the ditference of alti- 

 tude between the base of the mountains at Golden, Carbon, and the Parks is 

 not very considerable (Golden, 5,600 feet above the sea; Carbon, 6,750; 

 Middle Park, or Florissant, and South Park, at Castello's Ranch, about 8,500) ; 

 and the supposition also that the flora of the upper fourth group is that of 

 a mountainous region is apparently contradicted by the station of White 

 River, 4,600 feet of altitude only, which has the same flora as the Parks. 



I have left, for a conclusion of the remarks upon the age of the flora 

 of the Lignitic, the more important part referring to the general characters 

 of the lower group, a formation which has been and is still considered by 

 some geologists as Cretaceous; for it is advisable to have presented all together 

 the facts and observations which bear on this im^iortant subject. 



If we separate from the two hundred species ascribed to the first group 

 in the table of distribution those passing up to the other divisions, or those 

 which, either of frequent occurrence or of uncertain determination, cannot 

 Ijc considered as characteristic, and those, too, which, like the Fungi, do not 

 afford a reliable point of comparison, we find, in the Lower Lignitic flora, 

 one hundred and thirty species, which may be taken into account as record- 

 ing, by their characters and their relation, the age of the formation which 

 they represent. Of this number, twenty-seven are identical with Miocene 

 species of Europe, and forty are related to others of the same formation. 

 With the European Eocene flora, nine of the list are identical, and twenty- 

 eight related, while four are related to plants of the present time, five have been 

 described in the Mississippi flora, seven in tliat of Fort Union, and four from 

 Vancouver. Counting the plants of these three last stations as Tertiary, we 

 have, therefore, the Tertiary facies indicated by one hundred and twenty- 

 four specific forms, while only six represent the Crelaceous. This, it seems, 



