1 72 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA, 



\v(> havo six others, positively referable to this formation, one of wliirli is from 

 Vancouver, Iwo are common to the Mississippi and tlie Colorado Lii,niitic, and 

 two have been obtained from the lowest Tertiary strata of Point of Rocks, 

 which immediately rest upon the Cretaceous, and whose flora still preserves 

 a few representatives of Cretaceous types. In the Miocene of Europe, how- 

 ever, the genus takes a large predominance, twenty- eight species being there 

 described from this fwmation. To the present time, we have only ten ; but 

 considering the number of Tertiary species known from both continents, 

 this indicates about the same pro])ortion in the geological (iistril)uti()n. 

 Seven of the American Miocene species arc common with Europe; and, of 

 these, three are also found in Alaska They represent especially the Middle 

 Miocene, predominant in Oregon, and on the eastern side of the liocky 

 Mountains, especially at Carbon, a division from which comparatively few 

 materials have been obtained until now. As remarked in the descriptions 

 of the species, the relation of some of them to types of the present flora of 

 this country is distinctly recognized. 



§ I. — MarginatcR. 



Pop II I IIS lat ior, Al. Br., var. cordif olia. 



Plate XXII, Fig. 8. 



Populus latior cordif olia, Heer, FI. Tert. Helv., p. 12, pi. Iv.— Ludw., Falajont., viii, p. 91, pi. xxvi, fig. 7. — 

 Lesqx., Annual Report, 1871, pp. 287, 289. 



Leaves nearly round, broadei than long, sbort-JSointed, subtruncate at base, wavy-margined; 

 primary veins three, camptodromf. 



The form of this leaf and the characters of the borders arc referable to 

 those described by Heer, and the nervation, somewhat abnormal by the 

 absence of one of the primary nerves joining the midrib a little above the 

 border base, is comparable to that of the leaf figured by Ludwig. The upper 

 j)art of the leaf is destroyed. But another specimen, whose nervation is not 

 quite as distinct, described in the same Report, p. 287, as Populus latior var. 

 transversa, Heer, represents a smaller, short-pointed leaf, with more deeply 

 marked undulations of the borders, which is apparently referable to the same 

 variety. 



Habitat. — Washakie Station, Wyoming {Dr. F. V. Hayden). 



