Knowing where to look for fossils is a very important part of fossil
collecting. It has already been pointed out that igneous and metamorphic
rocks are not likely to be fossiliferous, but that most fossils are
found in marine sedimentary rocks. These sediments were deposited under
conditions that were favorable for organisms during life and which
facilitated preservation after death. Limestones, limy shales, and
certain types of sandstones are typically deposited under such
conditions.
One should look particularly for areas where rocks formed from marine
sediments lie relatively flat and have not been greatly disturbed by
heat, pressure, and other physical or chemical changes. If the rocks
appear to have undergone considerable folding and fracturing, there is
great likelihood that any fossils that were present have been destroyed
or damaged by this action.
Quarries are good places to look but one should be sure to obtain
permission before entering. Rock exposures in quarries are rather fresh
but have undergone some weathering. Quarries have been opened in many of
the limestone formations of Texas, and large numbers of fine specimens
have been collected in some of these excavations. Certain Lower
Cretaceous limestones are useful for road metal, building stone, or in
the manufacture of portland cement, and extensive quarrying has been
undertaken in the Edwards Plateau region of Texas (Pl. 9). Bones and
petrified wood are frequently found in sand and gravel quarries in many
parts of the State.
Particular attention should be given to all railroad and highway cuts as
rocks exposed in this way are usually still in their original position
and are fairly well weathered. Cuts made by recent construction are
usually more productive after they have undergone a period of weathering
as this helps to separate the fossils from their enclosing rocks.
Gullies, canyons, and stream beds are also good places to examine. These
areas are continually subjected to the processes of erosion or stream
action, and new material is uncovered year after year.
If there are abandoned coal mines nearby, the dumps of waste rock around
the mine shafts could be checked. A careful examination of such waste
may reveal fine specimens of well-preserved plant fossils.
Coal has been mined in several parts of Texas, and abandoned shafts or
dumps are still present in some counties. The bituminous coals of Texas
are predominantly Pennsylvanian in age, and mining has been carried on
in the following counties: Eastland, Erath, Jack, Palo Pinto, Parker,
Wise, Young.