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84 PLANT REMAINS IIS NOKTH AMEKICA.
Arancar'ui, and Salisburia ; tkey especially abound in genera still
bulking- largely in the flora of the United States. Among these may
be enumerated 7 sjiecies of Popnlus, 4 of Sallx, 6 of Quercus, 2 of
MofjnoUa, 2 of Plalanm, together with representatives of Biospyros,
Aridolochio, Sasftnfras, Liriocletiilron , Taxodium, Cupressus, etc., some
of which aie 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 difierence in the character of what w^as 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 uidike those of the continent at the present
day, the isothermal lines being siniihirly curved over the surface. It
would thus happen tiiat Palms and Cinnamons would, from the con-
ditions of temperature, be restricted to the western region of the Creta-
ceous continent.
IMany 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 Co^'nus^ Neguiido, Carya,
Sapindits, AraVia, Amelanchkr, Pluntra, Rhus, Sequoia, and Thnya.
The resemblance which this fossil flora bears to the living vegetation
of the United States is veiT 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 G lyploslrodiis, o? which there is a large num-
ber of specimens, and which cannot be distinguished from G. Enropcpiis ;
aiul other species (Taxodium dnbium, Ser/uoia Langsdorfii, etc.) are
very closely allied to European fossils, if they are not indeed identical
witli them.
From the Tertiary flora, w hen looked upon as the precursor of that
\\hich 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-
deiidioii, Liqiiiduinbar, Sumafras, etc., some of \\hich appear among the