sufficiently large to shrink significantly on drying are distinguished as pelo-
stagnogley soils (Greek pelos clay). Sandy soils are also distinguished at a high
categorical level. Soil textures are additionally described as stony or gravelly if
they contain 5 - 70 per cent by volume of stones.
Soils of the Forest
This account is based on semi-detailed mapping of 100 km2 west of
Brentwood on similar geology (Sturdy 1971), unpublished mapping of part of
Great Monk Wood and Deer Shelter Plain, and profiles described and analysed
for a recent excursion made by the British Society of Soil Science to the Forest
(Meeting Guide, Sturdy 1977) A schematised cross section in Fig. 3 illustrates
the relationship of soil series (the lowest unit of classification grouping soils with
similar horizon development and lithology) to landscape and geology. Table 2
gives analytical data for selected soil series.
Surface-water gley soils
Areally these are most important in the Forest reflecting the impervious
nature of underlying geological deposits. Soils from the three subgroups (i) pelostagnogley (ii) typical stagnogley and (iii) paleo-argillic stagnogley soils have
been recognised. Pelo-stagnogley soils are clayey throughout except perhaps for
a surface few centimetres of loamy material, and are represented by the
Windsor series (soil series are named after the locality where first described) in
London Clay and the Ragdale series in Chalky Boulder Clay. Whilst sharing the
common properties of shrinking and cracking when dried out in summer,
swelling when wetted up in autumn, and thence becoming only very slowly
permeable to winter rainfall leading to long periods of waterlogging, they can
differ slightly in their chemical properties. Slightly acid surface horizons of the
Ragdale soil (pH 6.3 in Table 2) quickly pass to a neutral to alkaline subsoil as
chalky clay is reached about 50 to 60 cm down, and earthworm activity is
vigorous with rapid incorporation of surface litter to give rise to mull humus.
Base saturation is high throughout with a characteristic rich flora including
primroses and dogs mercury, although much of the boulder clay area of the
Forest consists of outlying or peripheral grassy areas with tussock grass a
common sight. Such is Epping Long Green. Windsor soils are more acid at the
surface and have a thin mor humus horizon of lower base saturation. The
neutral subsoil reflects the presence of native calcium carbonate in the London
Clay, and contrasts with the non-calcareous clayey facies of the Claygate Beds
which can give rise to soils strongly acid throughout. These are a variant of the
Windsor series and can have a micropodzol development at their surface, as in
parts of Great Monk Wood under beech.
Occupying a large part of the area shown in Fig. 1 as Claygate Beds, and
some of the area shown as London Clay, is a typical stagnogley soil of the
Wickham series. This moderately or strongly acid soil consists of a thin mor
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