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Under the Surface
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Few places in the country demonstrate the connection between landscapes
and people better than the tallgrass prairie of the  Flint
Hills. The hills of the Tallgrass Prairie National Preserve
and the surrounding area are shaped by the rocks that lie
directly beneath the vegetation and soil - the same rocks
which made cultivation difficult and led to the use of native
prairie grasses for ranching. This rocky terrain is closely
tied to today's ranching culture.
The Flint Hills are characterized by thin soils, limestone outcrops,
vegetation-covered shale intervals between the limestones, deeply
incised valleys, and dissected topography. The Flint Hills cross
east central Kansas from the north near the Nebraska border and
extend into Oklahoma to the south. Many of the limestones contain
nodules and layers of flint (also called chert) - a hard, dense
rock that resists erosion. As the limestones erode, angular fragments
of flint accumulate at the surface, giving the Flint Hills their
name.
The thin, rocky soils and steep slopes of the Flint Hills have
precluded cultivation, effectively preserving the native grasslands.
Historically, only deep ravines and the flood plain of streams were
forested. Most cultivation is limited to river and stream bottoms,
such as along Fox Creek, just east of the ranch headquarters area;
there, the bedrock is covered by a layer of river-deposited sediments
that have developed thick soils that are especially valuable for
cultivation.
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Limestone ranges in color from nearly white to brown. It is hard,
and much more resistant to erosion than the softer shales, which
are usually gray or tan. The alternating beds of limestone and shale
produce hillsides with a terraced appearance. Many of the limestone
layers create notable benches on the hillsides; the shales form
the steep slopes between the benches. The hills themselves are created
by a process called differential erosion. Tougher, more resistent
limestones and flint cap the tops of the hills, while the land between
them has been worn away and slowly removed.
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| The rocks of this area - alternating beds
of limestone and shale - were deposited during the Permian Period
of geologic history, about 280 million years ago. At that time, the
climate here was hot, and the surface was covered by ocean water most
of the time. The limestones represent periods when the region's surface
was covered by shallow, tropical oceans which teemed with life/ shales
represent times when mud was deposited on the ocean floor. Each of
these sedimentary rock layers has been named after towns, creeks,
or other nearby landmarks; the names are based on the locations where
each rock layer was first found and described by geologists. |
A closer look at the rock reveals many fossils.
Most of these marine fossils are invertebrates - animals without
backbones- such as corals, clams, snails, bryozoans (colonies
of animals resembling sea fans), sea urchins, crinoids (a stalked
animal that is distantly related tothe starfish and sea urchin),
and clam-like animals called brachiopods. All of these organisms
at one time lived in a shallow, warm, tropical ocean. Particularly
abundant in some limestones are fusilinids - fossils shaped like
wheat grains; these were one-celled animals that floated in the
water. When they died, their skeletons drifted to the bottom of
the ocean and were preserved in the lime mud of the ocean floor.
These lime muds eventually became limestone. Fusilinids can be
seen in many of the limestone blocks used for building on the
preserve.
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