Figure 3. Schematic relationship of geology, soils and landscape in the Wake
Valley Region.
characterise old soils (Greek palaios ancient) whose formation began a long way
back in the past.
The rate of organic matter breakdown at the soil surface is partly con-
trolled by the water regime. Thus, thin surface organic horizons which are not
waterlogged for long periods are termed mor (raw) humus if sharply separated
from underlying mineral horizons, and mull humus if intimately mixed with the
mineral material. Gley soils sufficiently wet for a build-up of organic matter at
the surface are distinguished as humic groups or subgroups, but thick organic
accumulations in wet sites with little mineral content are classified as Peats.
Brown soils are not gleyed or are only slightly gleyed (stagnogleyic or gleyic
brown soils) and may also be argillic. Podzolisation is a complex process in
which a superficial layer of acid mor humus leads to development of a bleached
subsurface horizon, depleted of iron oxides, followed by darker horizons
enriched in organic matter (black) and in some cases iron (reddish brown).
Stagnogley podzols are recognised where an impermeable horizon at depth
causes some gleying in the profile.
The processes outlined above can apply to all silty, loamy, sandy or clayey
materials, but certain textural extremes are given recognition in the
classification. For instance, gley soils with a proportion of clay-size particles
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