60 



aud it is not surprising to find it already in tlie upper Cretaceous flora. 

 Its present distribution is mixed. Tbe genus preserves its predomi- 

 nance in Europe by the number of its species 5 it has there more than 

 a dozen, while Korth America has only four or five. 



It is remarkable that the next closely allied genus, Ceanothus, has not 

 yet been recognized in the Dakota group, though now an exceptional 

 American type. It has one species in the Eocene of Golden, another, 

 very fine, in the same formation of the Mississippi, and many more in the 

 upper Tertiary of the Eocky Mountains, and especially in the Pliocene 

 of California. The ten living species of true Ceanothus described in 

 the D. C. Prodromus, belong to the United States, especially to the 

 southern zone, aud a number of them are added to the list by the as 

 yet unpublished flora of California. The absence of the type in the 

 Cretaceous of the West is in accordance with the fact remarked upon in 

 describing the general character of the leaves of the Dakota group, viz, 

 the absence in this group of any kind of serrate leaves. 



It is uncertain whether the compound leaves of which a number of 

 separate leaflets have been figured in this memoir as Juglans Bebeyana, 

 represent a species of Juglans, or of Rhus. I am inclined now to refer 

 them to this last genus, especially on account of the nervationmore analo- 

 gous to that of the present Rhus meto])ium, of Florida,* whose leaves also 

 resemble somewhat the fossil ones ; but there is as yet no sufficient 

 evidence on this account. In considering the distribution of the species 

 of both Rhus and Jiiglans, in the' subsequent formations, we do not find 

 any difference pointing out to a predominance of one of these types at 

 any time. From the Dakota group, two other kinds of leaves are referable 

 to Rhus. In the upper Tertiary of the Eocky Mountains we have four, and 

 it iswellproved nowthatthe relationofoiu^ vegetable Cretaceous types is 

 not with Eocene species, but rather with those of the upper Tertiary and of 

 the present flora. On another side, Juglans acuminata and J. riigosa 

 which by their somewhat coriaceous entire leaves are distantly related 

 to the Cretaceous species, have been recognized at most of the locaUties 

 where Tertiary fossil plants have been found ; they are at Carbon and 

 also in the Eocene at Golden, the Raton, Black Butte, &c., and thus seem 

 to indicate by their general distribution the origin of Juglans in the 

 Cretaceous group as evidently as that of Rhus. From the Miocene of 

 Europe about twelve species of this last genus have been described, 

 two from the Arctic regions 5 and from the same formation as many 

 species of Juglans, with six species of Carya. At our time J. regia, so 

 generally known and cultivated for its large fruit, is of Asiatic origin, 

 while of the other four species known, three belong to the middle zone 

 of the United States, which has also for its share all the li^dng species 

 of Garya. Of the living species of Rhus, Austral Europe has two; one 

 of which, R. cotinus, has been compared by the form of its leaves to R. 

 emarginata of the Dakota group. We have in North America, besides 

 R. metopium, which is rather a tropical form, six species of the section 

 of the pinnately-divided leaves, with the trifoliate R. toxicodendron and 

 R. aromatica, both extremely variable, all types already represented in 

 the Pliocene of California. 



Except an Amelanchier, described by Dr. Newberry in his Notes on 

 Extinct Floras, &c.,from the Tertiary beds of the Yellowstone, we do not 

 know as yet any fossil species of Eosacete from the western Tertiary 

 measures. This is not a reason why Prunus should be excluded from 



* The species is indigenous in Cuba. I have specimens from South Florida, but it 

 may be there cultivated. 



