126 



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

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

 can 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 Rocky Mountains, and especially in the Pliocene of California. The 

 ten living species of true Ceanothus, described in De Candolle's Prodromus, 

 belong to the United States, especially to the southern zone, and 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 them are added to the list by the as yet unpublished flora of California.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 sepa- 

 rate leaflets have been figured in this memoir as Juglans (^) debeyana, represent 

 a species of Juglans or of Rhus. I should be inclined to refer them to this last 

 genus, especially on account of the nervation more analogous to that of the 

 present Rhus metopium of Florida, 1 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 Juglans in the 

 subsequent formations, we do not find any difference pointing to a pre- 

 dominance of one of these types at any time. Prom the Dakota group, two 

 other kinds of leaves are referable to Rhus. In the Upper Tertiary of the 

 Rocky Mountains we have six ; and it is well known now that the relation of 

 our vegetable Cretaceous types is not with Eocene species, but rather with 

 those of the Upper Tertiary and of the present flora. On another side, Jug- 

 lans acuminata and J. rugosa, which, by their somewhat coriaceous, entire 

 leaves, are distantly related to the Cretaceous species, have been recognized 

 at most of the localities 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 ; 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 



1 The species is indigenous in Cuba. I have specimens from South Florida, but it may be thero cul- 

 tivated. 



