This division has been divided into four subdivisions, among which are
many of the more common living and fossil plants. Such important plants
as the ferns, evergreens, hardwood trees, and the flowering plants are
all tracheophytes. Among the more common and abundant fossil
tracheophytes are the ferns, cycads, and _Gingko_, in addition to such
important “coal plants” as the scale trees, club mosses, and scouring
rushes (Pls. 12, 13). The latter commonly occur in many of the world’s
great coal deposits, and their remains make up a large part of the coal.
Plant fossils of this type may be collected in the dumps around some of
the abandoned coal mines in north-central Texas and from other
Pennsylvanian rocks in north and Trans-Pecos Texas.
[Illustration: Plate 11
GEOLOGIC RANGE OF THE MAJOR GROUPS OF PLANTS AND ANIMALS
The bands give some indication of the geologic range and relative
abundance of the major groups of plants and animals. An increase in the
width of the range band corresponds to a relative increase in numbers
during the corresponding portion of geologic time.]
PRECAMBRIAN
PALEOZOIC
CAMBRIAN
ORDOVICIAN
SILURIAN
DEVONIAN
MISSISSIPPIAN
PENNSYLVANIAN
PERMIAN
MESOZOIC
JURASSIC
CRETACEOUS
CENOZOIC
Thallophyta
Bryophyta
Tracheophyta
Protozoa
Porifera
Coelenterata
Bryozoa
Brachiopada
Mollusca
Annelida
Arthropoda
Echinodermata
Chordata
[Illustration: Plate 12
FOSSIL PLANTS]
[Illustration: THALLOPHYTES]
DIATOMS × 900
ALGAE × 400
[Illustration: TRACHEOPHYTES]
LEPIDODENDRON × ½
SIGILLARIA × ½
[Illustration: Plate 13
FOSSIL PLANTS
TRACHEOPHYTES]
NEUROPTERIS × ½
PSILOPHYTON × ⅓
CALAMITES × ½
AMELANCHIER × ½
CORDAITES × ¼
GINGKO × ½
Fairly well-preserved plant remains may also be collected from the
Woodbine group of the Upper Cretaceous in north Texas, and fossil wood,
most of it silicified, has been reported from rocks of almost all ages
and in almost every section of the State. In addition, some of the
carbonaceous clays and shales of east Texas contain large assemblages of
plant leaves, which in some places are well preserved.
It is also possible to find the fossilized remains of seeds, spores, and
pollen. Because of their small size, these minute remains are not
destroyed by the drill bit and can be brought out of deep wells without
being damaged, and for this reason they are a valuable tool for the
micropaleontologist.