55 



is referable to some forms of Populus attenuata, both these of the Miocene 

 and to the living P. nigra. Fopulites ovata maybe compared toPopuhis 

 mutahilis, also of the Miocene. On acconnt of the thick texture of the 

 leaves it is placed in the section marked Coriaceous, of which there is no 

 American representative atonr present time. The thickness of the leaves 

 of this last fossil PopuUtes is not much more marked than in the other 

 species of the genus. Scales of buds and seeds of poplars have generally 

 been found in the Miocene of Europe, in connection with leaves referable 

 to the genus. IS'one of these vegetable organs have been discovered as 

 yet in the shale of the Dakota group. The relation is, as remarked above, 

 indicated merely by the form of the leaves, and this character is scarcely 

 reliable to prove specific or even perhaps generic affinity. 



It is not the same case, however, with the leaves of Salix and of Fagus, 

 the willow and the beech. Their generic relation is positively indicated 

 by the form of the leaves and by their nervation. 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 tyx)e 

 is also represented in the Upper Tertiary or the Pliocene of California, 

 especially. The species of Fagus of the Cretaceous is, by its entire, undu- 

 late leaves, rather referable to the present F. sylvatica of Europe than to 

 onr F. ferruginea. Both these species, however, are so similar that they 

 were formerly considered by botanists as mere continental varieties, and 

 are still admitted as such by many. They have on both continents the 

 same wide and general distribution, being essential constituents of the 

 forests of our present time. The beech has representatives in far dis- 

 tant countries, but its types are local, and all the exotic ones differ 

 from that of our fossil species. Japan has one species with leaves cord- 

 ate at base and borders obtusely crenate, the secondary nerves tending 

 to the sinuses. Chili has five, with leaves obtuse, truncate at base, and 

 borders mostly doubly serrate. South Central America has one of very 

 wide distribution ; it has small coriaceous dentate leaves. New Zealand 

 has four, all with doubly serrate leaves and the lower surface white 

 tomentose ; and Tasmania has for its share two species of a still more 

 distant type, with obtuse, truncate, and dentate leaves. Per contra, 

 most of the species described as yet from the Tertiary are referable to 

 the European or the North American types. F. pristina is related to our 

 F. ferruginea. F. antipofi, from the Miocene of Alaska, is related to the 

 same by the slightly dentate borders, but differs indeed by the larger size 

 of the more taper-pointed leaves. F. macrophylla of the same formation 

 and country has the leaves entire, like the European spices, but still of a 

 far larger size, the specimen figured by Heer representing a leaf 16 to 18 

 centimeters long, and 10 centimeters wide, F. deucaUonis, F. feroniw, F. 

 horrida have borders of leaves more or less dentate, and therefore more 

 like the North American type. It is only when out of the geographical 

 limits of the north occidental flora or in the Grecian Archipelago that we 

 find a fossil species of Fagus related to an exotic form with doubly den- 

 tate small leaves: F. dentata, from ^uhea, a species which linger com- 

 pares to the Chilian F. ohliqiia. 



After this we find described from our Cretaceous flora : Betula heatri- 

 ciana, comparable by the form of its leaves and its nervation to our B. 

 nigra, so widely distribnted from the northern shores of Lake Superior 

 to Florida ; seeds of Myrica ; at least these which we have figured under 

 this name, are undistinguishable from Heer's seeds of Myrica described 

 from the Cretaceous flora of Quedlinburg, but indeed more flattened than 

 the seeds of any of our present species ; then leaves of oaks Quercus 

 primordialis, of the type of the so widely distributed and variable Q, 



