56 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [VolTL 



for the proper Eocky Mountains and the eastern plains no such summary- 

 is at hand, although Porter and Coulter's Flora of Colorado has brought 

 together some of the materials. 



We may estimate that the Atlantic flora north of the thirtieth parallel 

 (and wholly excluding Texas) consists of 850 PhsBuogamous genera and 

 3,400 species ; that the Pacific flora as now known does not exceed 620 

 genera and 3,000 species. Mr. Watson ten years ago had knowledge of 

 1,235 species in 439 genera (and 84 orders) in the Great Basin and the 

 adjacent Wahsatch and Uinta Mountains. If the ratio of genera and 

 species to orders is the same as in the Atlantic States, the whole Kocky 

 Mountain flora, from its eastern plains to the Sierra, and within the 

 designated parallels of latitude, would contain about 480 genera and 

 1,930 species ; and this is probably not far from the mark. 



The botanist will see at a glance the principal contrasts between the 

 Atlantic and Pacific floras. The Atlantic is the region of round-headed 

 and deciduous-leaved trees; the Pacific of spire-shaped, evergreen, 

 Coniferous trees ; and the Eocky Mountain forest is of the same type "as 

 that of the Pacific, only on a diminished scale, and with the more strik- 

 ing forms left out. 



The Atlantic flora has almost three times as many genera and four 

 times as many species of non-Coniferous trees as the Pacific, but it has 

 rather fewer genera and almost one-half fewer species of Coniferous 

 trees than the Pacific. 



The forest of the Atlantic States is, with one exception (that of jSTorth- 

 eastern Asia), much the most diversified, i. e., the richest in genera and 

 orders, as well as species, of any other temperate region. That of the 

 Pacific is one of the least diversified, except for its Coniferce. Both 

 together are remarkable for the persistence in them of certain peculiar 

 archaeological types of the latter, namely, Taxodium and Torreya on the 

 Atlantic side, Torreya, Liboeedriis, and, above all. Sequoia, on the Pacific. 



The Atlantic forest is of no inferior grandeur; few parts of the north- 

 ern hemisphere equal it in the stateliness of its trees, but the grandeur 

 of the Pacific forest growth as to Coniferous trees is wholly unequaled. 



These points have been brought out in a discourse by the present 

 writer (entitled Forest Geography and Archaeology), which was pub- 

 lished in the American Journal of Science and Arts, ser. 3, xvi, 1878, 

 and which, having been prepared in view of this report, it is proposed 

 to append the more important portions of it. 



There are certain orders or groups in which the diversification of 

 types and the number of forms in the Pacific flora much surpasses that 

 of the Atlantic, and it is to these that the salient features of the former 

 are mainly to be attributed; and in referring to these, the western 

 interior flora, sharing in these features, may be taken with the Pacific 

 flora x)roper. 



The largest of all the Phaenogamous orders, the Gom;positm, used to be 

 reckoned as constituting a tenth part of the Phaenogamous vegetation 



