Look at these rocks.
They have stripes!
These rocks were once sand
and mud at the bottom of a
shallow lake or sea.
Rivers brought the little
bits of rock down from the
mountains and spread them in
neat layers under the water.
that make up this cliff were once sand, silt, or
clay. Water captured
them by erosion and carried
the tiny particles into a lake or shallow sea.
Over millions of years these sediments were
cemented together by dissolved minerals or fused into rock by
the pressure of many more layers of sediment above them.
Layers are a sign that you are looking at
at this little hill. You can see that there are layers
of different colors. At one time this whole area was under
water. Streams brought silt and clay into the still water where
it settled in layers as the years went by.
are laid down as the seasons change. Wet seasons carry more sediment
than dry ones, so the result is a layered effect, like a pile
of papers. Some layers are very thin, some are thick. The colors
of the layers are caused by minerals: for example, reddish rocks
have been colored by iron.
in the colors of the layers are caused by the streams bringing
in a different kind of sediment. Geologists can
traces of ash from large volcanic eruptions in the rocks.
rocks preserve information from the distant past for us. Sometimes
they contain fossils. Fossils are the remains of animals and
plants that lived on earth many millions of years ago.
The layers in
the rocks tell us about long-ago changes in the landscape. Let's
look at how these rocks form and at what happens to them.
Sedimentary Rocks Formed?
Photographs from Corel CD-ROM
s: for viewing only, not for downloading.
1996,1997, 1998, 1999,
2000, 2002, 2003.
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