774 GEOLOGY OF THK YELLOWSTONE NATIONAL PARK. 



The excellent Flora n\' the Yellowstone National Park/ l)y Mv. Frank 

 Tweedy, has heen made rlic basis of all conijjarisons between the fossil and 

 livino- floras, ,'vccordini^- tn Tweedy, the present flora embraces 69 natural 

 families. '213 oenera. and (i.")7 species. The fossil flora emliraces 33 families, 

 1)3 ^-enera, and 148 species. The liyini;- flora has, therefore, 4 genera to 

 ea"li order and 2.4 sjjecies to each genus, while the fossil flora has not 

 cpiite 2 genera to each family and 2.3 S})ecies t() each genus, l^he relatiye 

 proportion between the families, genera, and s]iecies is shown to be approxi- 

 matel\' the same in the Tertiary and the living floras. A still further 

 CoiMparisun shows that there ai'e ;i fractinn more tluni twice as many living 

 as fossil families, 4..'! times as mam^ living genera, and 4.(1 times as many 

 species. 



On comjjaring the families in tlie two flm-as, it is found tliat 19 of the 

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

 families above gi^•en the ones not italicizeil are the families not repre- 

 senteil at the present time. It will be seen that sucli imjiortant families as 

 the Juglandace;e, Fagace;v, Ulmace;p, Magnoliacea', Laurace<i?, Plataiiacese, 

 Anaeardiacea?, Celastracea', Vitaceje, Sterculiaceie, Tiliacea?, Araliacepe, 

 Ebenace;i3, and ( )leacea! are not represented in the present flora. In other 

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

 sycamores, sumacs, grapes, lindens, aralias, persinniions, or ashes af the 

 present day. The alisence of such important trees and shrul)s prodiu-es a 

 profouml niodiflcation of the floral surroundings. 



The dominant element in the living flora consists of tlie abundant 

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

 are at all common, and (Jo 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 Srqudia srnijicrrirois i>f the Pacific coast. It 

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

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

 number ot sitpposed Sequoia cones. The })ines were also abundant, no 

 fewer \\v,\i\ 8 species having been detected. 



The deciduous-leaved trees and slu'uljs of the Yellowstone National 

 Park are conspicuously few in numliers. 'I'here are 2 species sif Betula, 2 



» Washington, 1886, pp. 1-78. 



