84 PLANT REMAINS IN NORTH AMERICA. 
Araucaria, and Salisburia ; they especially abound in geuera still 
bulking largely in the flora of the United States. Among these may 
be enumerated 7 species of Populus, 4 of Salix, 6 of Quercus, 2 of 
Magnolia, 2 of Platanus, together with representatives of Diospyros, 
Aristolochia, Sassafras, Liriodendron, Taxodium, Cupressus, etc., some 
of which are confined, as living plants, to the American continent, 
though they are found in Europe in Tertiary strata. The genera in- 
dicating a warm climate, like Sabal and Cinnamomum, are from the 
west coast ; while the Cretaceous beds of Kansas, Nebraska, and New 
Mexico have hitherto yielded no fossils of a tropical or even of a sub- 
tropical character. This difference in the character of what was pro- 
bably contemporaneous floras, is supposed to have been caused by the 
existence of an elevated central region separating the two sides of the 
broad continental surface on which the plants grew. This would give 
physical conditions, not unlike those of the continent at the present 
day, the isothermal lines being similarly curved over the surface. It 
would thus happen that Palms and Cinnamons would, from the con- 
ditions of temperature, be restricted to the western region of the Creta- 
ceous continent. 
Many of the genera found in these Cretaceous beds are represented 
in the Tertiary strata, and they are accompanied with numerous other 
forms, linking them still more closely with the vegetation of the pre- 
sent day. These comprise such genera as Cornus, Negundo, Carya, 
Sapindus, Aralia, Anelanchier, Planera, Rhus, Sequoia, and Thuya. 
The resemblance which this fossil flora bears to the living vegetation 
of the United States is very obvious. It agrees also to a considerable 
extent with the present flora of Japan and China, and with the fossil 
plants from the Miocene beds of Europe. Among the American Ter- 
tiary plants is a species of Glyplostrobus, of which there is a large num- 
ber of specimens, and which cannot be distinguished from G. Europeus ; 
and other species (Taxodium dubium, Sequoia Langsdorfii, etc.) are 
very closely allied to European fossils, if they are not indeed identical 
with them 
From-the Tertiary flora, when looked upon as the precursor of that 
which now occupies North America, several important genera are want- 
ing, which will most likely be yet discovered. Among the most 
striking of these deficiencies may be mentioned Acer, Quercus, Lirio- 
dendi on, Liquidambar, Sassafras, etc., some of which appear among the 
