Chapter 1
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13
fuels were formed from the fossils, or
remains, of dead plants and animals.
What natural forces caused our physical
features to form or change? Scientists
believe that rocks and soil deepbeneath the
earth’s surface slowly pushed against each
other to force up some of the earth. This
natural process is called
folding
. This is
oneway thatmountains are formed.
Scientists think that the
Appalachian
Mountain
chain began to form over 400
million years ago. The mountains that
cover parts of central Pennsylvania were
formed by this folding process. Remember,
folding is a very slow process. It took
perhaps two hundred million years for
these mountains to form. You can better
understand how folded land features form
by trying this idea. Get a tablecloth. Put
your hands about one foot apart. Slowly
push the tablecloth together for about three
inches. You should see mountains, ridges,
and valleys appear on the tablecloth.
Plateaus also can be formed by the
folding process. A large area of land is
pushedup above the surrounding land. The
Allegheny Plateau
was formed in this
manner. Sometimes, mountains with no
peaks form on a plateau. At 3,213 feet, our
highest point is
Mt. Davis
. Thismountain
is located in the southern part of the
Allegheny Plateau in Somerset County.
To the southwest of the
Allegheny
Mountains
, the
Laurel Highlands
lie.
These highlands are a group of mountain
ridges formed by the folding process. Two
well-known ridges in the highlands are
Chestnut Ridge and Laurel Hill.
Another natural force that changes land
features is known as
faulting
. Faulting
happens at aweakpoint in the earth’s crust.
It is similar to a “crack” in the land. This
crack or break in the land is called a fault.
When a section of land slowly moves, one
part rises above another. The other part
sinks to a lower elevation. The land near
Folding is one waymountains are formed. This folded landform is along I-80.
