[DL] “Monde des Plantes,” p. 197.
The leaves described by Heer, from the Middle Cretaceous of Greenland, are those of a poplar (P. primæva). Those which I have described from a corresponding horizon in the Rocky Mountains are a Sterculites (S. vetustula), probably allied to the mallows, and an elongated leaf, Laurophyllum (L. crassinerve) ([Fig. 69]), which may, however, have belonged to a willow rather than a laurel. These are certainly older than the Dakota group of the United States and the corresponding formations in Canada. On the eastern side of the American continent, in Virginia, the Potomac series is supposed to be of Lower Cretaceous age, and here Fontaine, as already stated, has found an abundant flora of cycads, conifers, and ferns, with a few angiospermous leaves, which have not yet been described.
Fig. 69.—Stercalia and Laurophyllum or Salix, the oldest Angiosperms Known in the Cretaceous of Canada.
In the Canadian Rocky Mountains, a few hundreds of feet above the beds holding the beforementioned species, are the shales of the Mill Creek series, rich in many species of dicotyledonous leaves, and corresponding in age with the Dakota group, whose fossils have been so well described, first by Heer and Capellini, and afterward by Lesquereux. We may take this Dakota group and the quader-sand stone of Germany as types of the plant-bearing Cenomanian, and may notice the forms occurring in them.
In the first place, we recognise here the successors of our old friends, the ferns and the pines, the latter represented by such genera as Taxites, Sequoia, Glyptostrobus, Gingko, and even Pinus itself. We also have a few cycads, but not so dominant as in the previous ages. The fan-palms are well represented, both in America and in the corresponding series in Europe, especially by the genus Sabal, which is the characteristic American type of fan-palm, and there is one genus which Saporta regards as intermediate between the fan-palms and the pinnately leaved species. There are also many fragments of stems and leaves of carices and grasses, so that these plants, now so important to the nourishment of man and his companion animals, were already represented.
Fig. 70.—Vegetation of Later Cretaceous. Exogens and palms. (After Saporta.)