420 ■ GEOLOGICAL SURVEY OF THE TERRITORIES. 



131 per cent, of its species in common with Alaska, 20| per cent, with 

 the Arctic flora, 40 i3er cent, with the Miocene ; and our Lower Eocene 

 has only 8| per cent, of its species in common with the Alaska, 10| per 

 cent, with the Arctic, and 25 per cent, with the European Miocene. 

 Or counting the species of Alaska, Arctic, and Miocene of Europe as 

 Miocene, the relation of the American Tertiary flora with this forma- 

 tion of Europe is, for the Miocene, 47f ; the Upper Eocene, 57^, and 

 for the Lower Eocene, 37 per cent. 



This comparison, somewhat unreliable on account of the greater or 

 less degree of affinity of a few species, may be, however, admitted in 

 full confidence for our purpose^ and proves that the flora whiph we con- 

 sider as representing our Miocene, that of Green Eiver, Elko, and South 

 Park, does not bear to that of Eurojje a marked analogy by its forms. 

 These, indeed, appear of younger type, more intiuiately related even by 

 identity to species of our time. The flora of the group marked as Upper 

 Eocene has, per contra^ the 'greatest analogy to that of the European 

 Miocene by the identity of its most common species of Populus, Quercus, 

 JJlmus, Betula, Flatanus, Fagtis, &c. It may be that farther researches 

 may force a separation of this group from the Eocene, though as yet 

 there is no apparent line of division, either in the measures or in the 

 distribution of the flora. I believe that the discrepancy is merely 

 apparent, resulting from and indicating a precedence in time of our 

 botanical types over those of Europe. This fact has already been re- 

 marked upon in considering the flora of the Carboniferous formations, 

 and it becomes the more evident as the history of the old vegetable 

 world is better known. The relation of the Lower American Eocene to 

 the Miocene of Europe, 37 per cent., does not indicate a difference more 

 marked than could be expected between the flora of two members of 

 the same formation ; and the difference, too, is becoming more and 

 more definite, and will continue in the same way as far as the acquaint- 

 ance with our fossil flora is more intimate. The most common species 

 of fossil-plants are not only found over wide areas, and therefore col- 

 lected from all the explorers, and in numerous specimens ; but they i)ass 

 through the different stages of the formations. The first researches 

 bring them to view from everywhere 5 the selection, however, becomes 

 more discerning and exclusive in proportion to the amount of materials 

 supplied for comparison. 



On the question of the distribution of Tertiary fossil'species in regard 

 to climatic circumstances, the table does not show anything more than 

 what has been observed from that of the former report. The relation 

 of our Upper Eocene flora with that of Alaska and Greenland is well 

 defined, while the vegetable types of the Lower Eocene are rather trop- 

 ical than Arctic. It is then possible that the characters which I have 

 considered as resulting from climatic influences have a relation to differ- 

 ence of age of the formations. If it is the case, we may expect to find 

 the flora of the Lower Eocene with the same southern types from Van- 

 couver Island to the Mississippi, while the Arctic facies may predomi- 

 nate in the Upper Eoceue from Greenland to the same southern latitude. 



This important question of the regulation of Tertiary grouj)s of vege- 

 tables according to their geological stations, or to climatic influences, 

 cannot be settled without loug researches. Some si)ecies of the Lower 

 Eoceue appear to have, with types of the present flora of Cuba, a 

 relation which has not been recognized before. Such are forms of 

 Flahellaria and Calamopsis ; Myrica Torreyi, compared to a Lomatia ; a 

 group of Ficus, represented by Ficiis ijlanicostata, F. Clinto7ii^ F. spec- 

 tabilis, F. corylifolia; — Cissus IcevigatnSjAleurites FJocenica,a,nil the group 



