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778 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



tory species, was not abundant or particularly important. The most abun 

 dant form (E. haguei) is small and has much the appearance of the living 

 E. limosum. The largest form (E. microdontuni) is very rare. It was 

 about 3 cm. in diameter. 



From what has been presented, it is obvious that the present flora of 

 the Yellowstone National Park has comparatively little relation to the 

 Tertiary flora, and can not be considered as the descendant of it. It is also 

 clear that the climatic conditions must have greatly changed. The Ter- 

 tiary flora appears to have originated to the south, while the present flora 

 is evidently of more northern origin. The climate during Tertiary time, as 

 made out by the vegetation, was a temperate or subtemperate one, not unlike 

 that of Virginia at the present time, and the presence of the numerous species 

 of Ficus would indicate that it even bordered on subtropical. The condi- 

 tions, however, that permitted the growth of this seemingly subtropical vege- 

 tation may have been different from the conditions now necessary for the 

 growth of these plants. Thus, the genus Dicksonia is at present a tropical 

 or subtropical genus, yet at least 1 species is distributed well into the tem- 

 perate region. If a series of beds should be discovered in which there were 

 a large number of Dicksonias, it might be supposed to indicate tropical or 

 subtropical conditions; yet, as a matter of fact, these species may at that 

 time all have been so constituted as to grow in a temperate land, and the 

 genus as a whole may have become tropical in recent times. Following- 

 out this general line of argument, it may be said that while the Tertiary 

 vegetation of the Yellowstone National Park would, from our present 

 standard, be regarded as indicating a temperate or possibly warmer climate, 

 the actual conditions then prevailing may have been quite different. It is 

 certain, however, that the conditions were very different from those now 

 prevailing. 



