Translocated (oxalate-soluble) A1 and Fe are present predominantly in inorganic forms in the B, horizons of the five pcdzol profiles examined: A1 as imogolite and proto-imogolite allophanes, and Fe as a separate oxide phase. Below the top few cm of the B, horizon, over 75 per cent of the extractable (acid-plus alkali-soluble) organic matter is present as Al-fulvates, largely sorbed on allophanic material. The Bh horizons of the Iron Humus Podzol and Iron Podzol intergrades are distinguished by very high levels of organically bound Fe (soluble in EDTA solution), five to ten times more than in immediately adjacent A, or B, horizons, and also by larger humic acid contents than in comparable B, levels in typical Iron Podzols. Inorganic forms of translocated A1 and Fe are probably absent from two of the three Bh horizons examined, and also from the Bhg horizon overlying the thin iron pan in the Peaty Podzol. The organic matter in this Bhg horizon is saturated with Al rather than Fe. Chemical and physical processes which could lead to evolution of a profile along the genetic sequence, Iron Podzol, Iron Humus Podzol, Peaty Podzol, are postulated.

Eskbank Nurseries, a market garden allotment some 200 m long and 30 to 40 m wide, lies at approximately 70 m OD on a relatively level terrace overlooking the south bank of the river North Esk (fig. 1). The excavated area is centred on NT320660 and lies within the two superimposed Roman camps first noted as crop marks by St Joseph in 1965 and subsequently excavated by Maxfield in 1972. Her excavation areas I and II were sited to investigate a pit alignment, visible on the aerial photographs and plotted by her (Maxfield 1974, 142, fig. 1). In the event no pits were discovered by excavation, a fact attributable to an unfavourable combination of weather and soil conditions (Maxfield 1974, 150). The pit alignment did not, of course, appear as a crop mark in the deep market-garden soils of the Nurseries but, by extrapolation of Maxfield's plot, it was clear that it must cross the northern half of the allotment, possibly intersecting the north ditch of the earlier of the Roman camps (Maxfield's Camp A) on the west edge of the site.

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Infrared spectroscopy and chemical degradation indicated several fulvic acid fractions from an iron-humus podzol capable of complexing and translocating metals. Acidic polysaccharides, some of them resembling pectic acid, were isolated in appreciable quantities. These are able to bind metals through carboxyl groups, but peptide components present in the polysaccharide fraction may provide alternative metal complexing centres. The high yield of acidextractable organic matter from the illuvial humus, together with its high content of carboxylic acid groups, make it likely that this fraction plays a major role in the translocation of metals. Phenolic compounds allegedly associated with this process were present in the fulvic acid solution in low amounts, and only in the extracts from the organic horizons.In trod u c tion THE term 'podzol' originally implied the occurrence of a bleached A2 layer below the surface horizons of the soil profile (Muir, 196 1). Wider definitions of the term include features which may be more obvious in the field, for example the existence of an ochreous B horizon containing translocated humus (cfi Romans, 1 970). The accumulation of humus in the B horizon, accompanied by relatively high concentrations of aluminium and iron, has been held t o indicate an organic complexation and translocation of mineral cations. Indeed, laboratory experiments involving leaf leachates (Bloomfield, 1970), and field studies on the composition of canopy drip and the movement of sub-surface soil water (Davies, 1 970) have demonstrated the feasibility of such hypotheses.Soil organic matter is also likely t o be important in this type of translocation, particularly the more soluble, lower molecular weight, fulvic acid fraction. Forsyth (1947) introduced a method of fractionating fulvic acid solutions based on adsorption of the mixtures on charcoal and the subsequent elution (by various solvents) of fractions A, B, C and D. The aim of the present study is to characterize these Forsyth fulvic acid fractions from a podzol under natural vegetation, using infrared spectroscopy and chemical degradation, and t o deduce whether they are capable of complexing and translocating metal ions. A preliminary account of this work has already beep given (Anderson, 1970).