An enumeration of the kinds of trees that are represented by the woods
in the fossil forests of the Yellowstone National Park will naturally be
demanded. A superficial or macroscopic examination of these trunks would
not permit a close decision as to the kind of wood: in fact, it would
hardly be possible to do more than separate them by this means into
coniferous and dicotyledonous trees. But by studying thin sections under
the microscope it is possible to distinguish the different kinds with
reasonable accuracy. As the result of such study the following species
have been detected:
Magnificent redwood (Sequoia magnifica).
Alderson’s pine (Pityoxylon aldersoni).
Amethyst pine (Pityoxylon amethystinum).
Laurel (Laurinoxylon pulchrum).
Aromatic bay (Perseoxylon aromaticum),
Hayden’s sycamore (Plantaninium haydeni).
Knowlton’s sycamore (Plantaninium knowltoni).
Felix’s buckthorn (Rhamnacinium radiatum).
Lamar oak (Quercinium lamarense).
Knowlton’s oak (Quercinium knowltoni).
Although only three kinds of coniferous trees have thus far been found
in the fossil forests of the park, fully 95 per cent of all the trunks
belong to these three species. The preponderance of conifers is probably
due to the facts that they were presumably more abundant in the
beginning, and that, in general, coniferous wood decays less rapidly
than that of most of deciduous-leaved trees. But the conditions were so
favorable for preserving any wood that it is perhaps strange that not
more trunks of deciduous-leaved trees have been found there. As it is,
however, a greater number are known from the park than from any other
region. Thus, the Arizona fossil forests embraced only two species of
deciduous-leaved trees: the Calistoga (California) wood only one
species, and the forest at Cairo, Egypt, only four species.
The 10 species of trees represented in the fossil forests of the park
are by no means the only fossil plants that have been found. The
fine-grained ashes and volcanic mud in which the forests were entombed
contain also great numbers of impressions of plants, many of them very
perfectly preserved. Most of these are impressions of foliage, such as
fronds and leaves, but they include also roots, stems, branches,
fruiting organs, and even what is believed to be the petals of a large
magnolia flower. About 150 different kinds of fossil plants have been
found in the park, 80 in the same beds with the forests, and most of the
others in slightly higher and younger beds. The list embraces 10 ferns,
among them a fine chain fern (Woodwardia), several aspleniums, and a
beautiful little climbing fern (Lygodium). The horse-tails (Equisetum)
are represented by 4 species. The conifers include no less than 6
species of pines (Pinus), a yew (Taxodium), and 2 sequoias. These have
been identified either from the foliage or the cones, and it is more
than likely that some of the specimens may represent organs that
belonged to trees represented by the fossil trunks, but as they have
never been found connected they have been described separately. The
monocotyledons, or plants with parallel-veined leaves, are represented
by only a few forms, such as a single large grass (Phragmites), a few
sedges (Cyperacites), a smilax, and a curious broad-leaved banana-like
plant (Musophyllum). The dicotyledons, or deciduous-leaved plants, make
up the bulk of the flora and include walnuts (Juglans), hickory nuts
(Hicoria), bay berries (Myrica), poplars (Populus), willows (Salix),
birches (Betula), hazel nuts (Corylus), beech nuts (Fagus), chestnuts
(Castanea), oaks (Quercus), elms (Ulmus), figs (Ficus), breadfruits
(Artocarpus), magnolias (Magnolia), laurels (Laurus), bays (Persea),
cinnamons (Cinnamomum), sycamores (Plantanus), acacias (Acacia), sumachs
(Rhus), bittersweet (Celastrus), maples (Acer), soap berries (Sapindus),
buckthorns (Rhammus), grapes (Cissus), basswood (Tilia), aralias
(Aralia), dogwoods (Cornus), persimmons (Diospyros), ash (Fraxinus), and
a number of others without vernacular names.