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Formation
of Cutover and Cutaway Bogs
The cutaway
and cutover bogs of the midlands of Ireland were originally raised
bogs. Raised bogs have a complex history of growth and formation
spanning some 10,000 years. The different layers in the peat
bog exposed by turf cutters record the different stages in the
growth of the bog over this time. At the top of the bog there
is brown acid peat. This is divided into two layers. The younger
Sphagnum peat is on the surface. Below this is older,
more decomposed Sphagnum peat which contains the fibrous
remains of bog cotton. Beneath the acid peat is fen peat, which
is dark brown to black in colour. There are three peat types
found. Woody fen peat with the remains of pine and birch wood,
peat with abundant remains of bog bean, and reed peat. The total
depth of peat in a raised bog can be as much as 15m. The ground
beneath the peat mass is not flat. There are depressions and
ridges. The sub-peat mineral soils comprise silty clay soils,
silt, weathered and unweathered glacial till soils, gravel and
lake marl.
The interpretation
of the soil and peat types exposed by turf cutting show that
raised bogs began to grow in depressions which were occupied
by lakes. Slowly plants colonized the open water, their dead
remains or peat completely filling in the depression to form
a fen. Once the depressions were filled with dead plant material,
the peat spread over the mineral soil ridges in between the depressions
and continued to accumulate in a great heap called a raised bog.
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