Bogs
are primarily composed of water and peat (which is decaying
plants).
Bogs
have different layers of peat. A cross section of a bog
shows that the peat layers change color. 
The lighter peat (weisstorf in German) is chunkier; the
dead plants in it have decomposed less. This peat is called
peat moss and is used primarily for gardening (though it has
been used in animal pens since it's much more sanitary than
straw). The darker peat (schwarztorf in German) is much
denser and used for heat and fuel.
Peat
is cut in chunks, called mumps. Mumps are stacked, sometimes
in elaborate piles, to dry. 
When
dry, the peat can be processed for industrial or medicinal
purposes or burned. It is also used to produce charcoal.
In the past,
the people of northern Europe (where many bogs were once
found) would go into the bogs to dig peat. 
First, they would drain the upper level of water to a lower
area. Then they used shovels and special peat saws to cut the
peat and dry it for use. After the industrial revolution,
they might build a small rail track so that a larger number of
mumps might be hauled at one time. Eventually, they began to
use machines to help them cut. 
Early machines were smaller; these were followed by huge
machines that could cut a great deal of peat. Of course the
more peat that was cut, the more bogs were destroyed. 
Today very few bogs exist in northern Europe. In Germany,
attempts have been made to regrow bogs, but this is a very
slow process. A raised bog may grow a millimeter in one year's
time.
Sometimes,
as people cut peat in bogs, they found things that had been
placed there long ago. 
They
found wonderful objects--necklaces, swords, or even silver
cauldrons. And sometimes they found the gruesome,
preserved remains of human beings: men, women, and children.
Note:
Preserved bodies have been found only in the bogs of northern
Europe.
