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(lenticulation cannot be remarked on account of the coarseness of the stone 

 imbedding the leaves. We could give the same reason or admit such a 

 supposition, but the form of the leaves of this genus is so peculiar that 

 the difference in the more or less serrate borders cannot prevent a generic 

 identification. The leaves of the Cretaceous species are, especially by 

 their truncate base and their general outline, rather related to those of our 

 L. styracifluum than to those of the Asiatic form, L. orientate. These are 

 the two only living species of Liquidambar with palmately-lobed leaves. 



The history of this genus, its origin, and the present distribution of its 

 species, offer, with that of Platanus, a coincidence worth remarking. Both 

 appear first in the Dakota group ; both pass through the Tertiary formations 

 of Europe in different modifications ; and both have each for essential 

 representatives of the present flora an oriental and an occidental form : in 

 Asia, Liquidambar orientate and Platanus orientalis ; in our country, L. sty- 

 racifluum and P. occidentalism of which the Mexican and the Californian 

 forms are mere derivations. No species of Liquidambar has been as yet 

 recognized in our North American Tertiary formations. Two species widely 

 distributed are described with numerous varieties from the Tertiary of Europe. 



The leaves referred in this memoir to the genus Populites are not com- 

 parable to any of the North American species of Populus of our time. 

 They especially differ by the entire borders, which in all our species are more 

 or less serrate or dentate. By this character, as well as by their coriaceous 

 substance, the relation of the Cretaceous species of Populites is with a peculiar 

 group of poplars, the Coriacea, represented in the Upper Miocene of Europe, 

 and with us at Evanston and Carbon, by Populus mutabilis and P. gaudini, 

 Heer, and at this time by P. euphratica, Oliv., an oriental species, whose 

 leaves, however, are dentate, and P. pruinosa, Schr., of Siberia, whose leaves 

 are nearly round, with borders entire. This last one only may be said to 

 have a marked relation to the Populites of the Dakota group. 



The relation, however, of Salix and Fagus with present species of our 

 flora is positively marked. Our Salix Candida, Wild., as widely distributed 

 as a shrub as the beech is as a tree, is the living willow most intimately 

 related to the Cretaceous form. Its type is also represented in the Upper 

 Tertiary, or the Pliocene of California especially. The species of Fagus of 

 the Cretaceous is, by its entire, undulate leaves, rather referable to the present 

 F. syloatica Of Europe than to our F. ferruginea. Both these species, how- 



