Peat deposits and the lake sediments which
sometimes underlie them have
enormous value as historical records of conditions, both physical and biological,
going well back into the Quaternary Period. Both direct stratigraphical studies,
involving examination of subfossil plant and animal remains, and pollen analysis,
supported by the technique of radio-carbon dating, have built up the ecological
history of the British Quaternary as summarised by Godwin (1956,1975)-
Soligenous mires are of negligible historical
interest, for their peat is usually very
shallow and much influenced by downwash of material or other disturbance. Valley
mires are mostly of relatively little value, for similar reasons, though some examples
with deep peats and underlying Post-glacial sediments are notable exceptions.
Most blanket mires began to form at the onset of the wet Atlantic Period or later,
and the deepest deposits contain particularly good records of vegetational history
during this part of the Postglacial Period. The peat of blanket mires often contains
abundant buried tree remains, especially of pine, birch and willow, at various
horizons, giving valuable direct evidence of former forest composition and tree
growth at the particular sites. The most valuable stratigraphic sequences are in
certain basin mires and raised mires which formed on the sites of ancient lakes
and contain basal Late-glacial and Post-glacial sediments, often overlain by fen
peat, and finally by a thick layer of acidic mire peat, usually rich in Sphagnum
remains.
It is therefore necessary to ensure that
the peat deposits of greatest historical
significance are included in the series of nationally important peatland sites. In
some cases, these peats are associated with underlying mineral deposits which
represent an integral and earlier part of the stratigraphic sequence. The scientific
value of sediments in their own right will, however, be considered in a separate and
subsequent evaluation of geological and geomorphological features. Many of the
peatlands which are of outstanding importance for their morphological and surface
features are also valuable for their historical content, so that the lists to be
presented take account of this interest to a considerable extent.
