774 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



The excellent Flora of the Yellowstone National Park, 1 by Mr. Frank 

 Tweedy, has been made the basis of all comparisons between the fossil and 

 living- floras. According to Tweedy, the present flora embraces 69 natural 

 families, 273 genera, and 657 species. The fossil flora embraces 33 families, 

 63 genera, and 148 species. The living flora has, therefore, 4 genera to 

 each order and 2.4 species to each genus, while the fossil flora has not 

 quite 2 genera to each family and 2.3 species to each genus. The relative 

 proportion between the families, genera, and species is shown to be ajaproxi- 

 mately the same in the Tertiary and the living floras. A still further 

 comparison shows that there are a fraction more than twice as many living 

 as fossil families, 4.3 times as many living genera, and 4.6 times as many 

 species. 



On comparing the families in the two floras, it is found that 19 of the 

 33 fossil families are not represented in the living flora. In the list of 

 families above given the ones not italicized are the families not repre- 

 sented at the present time. It will be seen that such important families as 

 the Juglandaceae, Fagacese, Ulmaceae, Magnoliacese, Lauracea?, Platanacea?, 

 Anacardiaceae, Celastraeea j , Vitacese, Sterculiaceae, Tiliacese, Araliaceae, 

 Ebenacese, and Oleaceaj are not represented in the present flora. In other 

 words, there are no walnuts, beeches, oaks, chestnuts, elms, magnolias, 

 sycamores, sumacs, grapes, lindens, aralias, persimmons, or ashes at the 

 present day. The absence of such important trees and shrubs produces a 

 profound modification of the floral surroundings. 



The dominant element in the living flora consists of the abundant 

 coniferous forests; yet only 8 species are represented, and of these only 5 

 are at all common, and 65 per cent of the whole coniferous growth is made 

 up of 1 species. The fossil flora is represented by 13 species, or nearly 

 twice as many as the living. Among them was a magnificent Sequoia that 

 was closely allied to the living Sequoia sempervirens of the Pacific coast. It 

 had trunks 10 feet in diameter and probably of vast height. There were 

 also 2 well-marked species of Sequoia, known from the leaves, and a 

 number of supposed Sequoia cones. The pines were also abundant, no 

 fewer than 8 species having been detected. 



The deciduous-leaved trees and shrubs of the Yellowstone National 

 Park are conspicuously few in numbers. There are 2 species of Betula, 2 



1 Washington. 1886, pp. 1-78. 



