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| Ron Allen's soil and water pages |
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I visited Parndon Wood, near Harlow in Essex, in October 1974 to describe the main soils and their characteristics.
This ancient woodland which has Oak standards over coppiced Hornbeam is a Site Special Scientific Interest (SSSI) that was purchased by Harlow Council in 1968, and became a Local Nature Reserve by agreement with the Nature Conservancy Counil in 1974.
The survey involved hand augering the soils using a 1.2m long Edelman soil auger at 31 locations and describing the soil characteristics of each horizon.
Here is a summary of my report (updated slightly where necessary). A map is available separately.
Hydrology and Landform
Parndon Wood lies within the catchment of the Parndon Brook and straddles a minor tributary of that stream. The wood lies on the northfacing slope of the interfluve dividing the catchments of the Parndon and Cobbin's Brooks. There is a maximum relief of 100ft and at its highest point the reserve attains 350ft. The wood serves as a surface water run-off collection area for the minor stream as the associated small valleys are cut into clayey material of very low permeability.
Geology
The 'solid geology' of the South Harlow area is of London Clay, a marine or estuarine clay deposited during the Palaeocene or Eocene period the Tertiary, some 60,000,000 years ago.
On the interfluves and higher parts of the landscape, a glacial chalky till is found. This is thought to have been deposited by melting ice during the Anglian State of the Pleistocene Ice Age, some 80-90,000 years ago.
These two deposits form the substrate of Parndon Wood and the parent materials of the woodland soils. The bulk of the wood is on London Clay, while the highest land to the south is on the chalky glacial till.
The London Clay is a stiff smooth clay of a brownish colour in its upper part and generally grey or bluish at depth. In the wood it is of its characteristic chocolate brown colour. It is extremely sticky and tenaceous when wet and is well seen on the steeper slopes of the wood where thereis no covering of leaf litter.
The chalky glacial till is greyer, weathering at the surface to brown. While clayey, it is a lighter, more silty and sandy clay than the very heavy and sticky London Clay. The clay contains a high proportion of chalk pieces and occasional flint stones. The unweathered till, at depth is highly calcareous and can be seen in the ditch at the south end of the wood. The till is commonly known as the Chalky Boulder Clay.
Soils
All the soils on the reserve are slowly permeable and affected by surface waterlogging in winter indicated by some degree of grey and ochreous (orange) mottling, particularly near the surface. Those soils that are dominantly grey with ochreous mottles near the surface are Surface-water gley soils (Stagnlogley soils) affected by prolonged seasonally surface waterlogging. Those with less grey and ochreous colours are Brown soils (in this case Stagnogleyic brown earths) and waterlogged for shorter periods in winter.
Particular combinations of parent material, texture and water regime (amongst others) produce recognisable soil units or profiles as seen in vertical (as in a pit). A group of similar profiles (having areal extent) are called soil series and given names.
Soils on the London Clay
The most common soil on the London Clay at Parndon Wood is the Windsor series, a Surface-water gley soil (Stagnogley soil) with grey and ochreous mottles in the upper soil layers. The soils are clayey to the surface and shrink and swell seasonally often creating deep vertical cracks. Such swelling clayey soils are known as Pelostagnogley soils.
In the bottom of parts of the valleys, the upper layers of the soil have a higher proportion of organic matter creating unnamed humic-stagnogley soils.
In places on the reserve, there are surface accumulations of lighter textured clay loam material overlying the London Clay and which have a higher proportion of sand and silt and are often flinty in their upper layers. These soils do not shrink and swell to the same exent and are known as the Wickham series.
Soils on the Chalky Glacial Till
These soils are also clayey and, on the reserve, the chalk has mostly been leached to at least 50-60cm depth and sometimes deeper. The surface layers are non-calcareous and calcaeous chalky material only ocurrs at depth. These soils also crack in summer and are known as Ragdale series (pelostagnogley soils).
In places, leaching has been less extreme and chalk pieces are found within the upper 40cm (often to near the surface) and the soils are mostly calcareous throughout the profile. These Hanslope series soils (typical calcareous pelosols)are browner with fewer grey mottles than the Ragdale series indicating less frequent waterlogging.
Thin spreads of flinty loamy material also occur in the glacial till area giving rise to seasonally waterlogged loamy over clayey Beccles series soils.
Most soils on the reserve are neutral or slightly acidic in their woodland topsoils. Hanslope soils can be calcareous at the surfaces.
More Information
More information on the geology and soils of the types occurring in Parndon Wood can be found in:
C A H Hodge, R G O Burton, W M Corbett, R Evans and R S Seale Soils and their use in Eastern England published by the Soil Survey of England and Wales as Bulletin No. 13 in 1984.
More information on the reserve can be found on www.harlow.gov.uk.
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The Environmental Project Consulting Group
44A Winchester Road, Petersfield, Hampshire GU32 3PG
email: Ron Allen, tel: 01730 231019,
Copyright April 2005 Ron Allen
Geologist, Soil Scientist, Applied Ecologist, Hydro-ecologist, Chartered Environmentalist
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