Dr Smithson , I think it was , mentioned the evidence to be obtained through the examination of stones . their orientation will give a sense of the direction of movement and often a good deal can be learned from the kind of stone . I would make a plea here that I have heard Dr Smithson make so often . a stone , if it is to be examined at all , deserves it only after it has been scrubbed clean in the laboratory , and indeed after the macro-examination efforts might profitably be extended to microscopic examination of a thin section . as to the examination of stones in a soil profile , I would repeat my own rather stale and weary warning . stones in a soil profile are those things that have failed to weather to form a soil . do not ignore them but at least pay them less attention than the fine fractions . let us suppose that we have succeeded in making a full assessment of a parent material . we are still left with many other factors which will ultimately influence the processes of profile formation . there are ( a ) the topography of the site which influences drainage , surface run-off and the chances of erosion , ( think of this in relation to the mass of debris left after the retreat of the ice sheet ) , ( b ) the climate within the developing profile - a composite of temperature , rainfall , evaporation and transpiration and drainage . ( a ) and ( b ) indirectly influence ( c ) the kind of vegetation which can in turn check the processes of decay and leaching in some cases and in others hasten them . sets of slides were then shown to illustrate the effect of : - ( 1 ) . altitude . parent material : Silurian shale drift . ( a ) . at 1,200 above sea level producing peat , peaty gley and gley podzolic and slightly podzolic profiles . ( b ) . at 250 above sea level . brown forest soil of good base status . ( 2 ) . rainfall . common parent material sandy textured drift of mainly carboniferous limestone . Co Roscommon , Ireland . 45 -50 mean annual rainfall &amp;symbol; podzol . Co Meath 30 mean annual rainfall , high base status , brown forest soil . ( 3 ) . vegetation . site Knightwood inclosure , New Forest , Hampshire . parent material Barton sand . planted 1860 oak &amp;symbol; low base status , brown forest soil . Scots pine &amp;symbol; deep humus podzol . soil development on drift deposits of the Welsh borderland . by D MacKney . since little pedological investigation has been directed to drift deposits of the Welsh borderland , outside certain areas in Shropshire and Cheshire , this discussion of soil development is centred on the Cheshire-Shropshire plain . for the most part this plain is below 300 ft , abutting to the west against the eastern uplands of Wales and in the south fringing the pre-Cambrian and Palaeozoic rocks of the south Shropshire uplands . this gently undulating , sometimes flat surface masks an extremely complex series of glacial deposits which are often very thick , so that only a few isolated ridges of Trias sandstone obtrude . the glacial events which have led to the formation of the midland plain are controversial in detail , but some conclusions are universally accepted . the deposits which form the plain have been derived from the Palaeozoic rocks of Wales and the north , as well as from the underlying Triassic rocks . however it is probable that a good deal of the surface layers of drift have been affected by sorting and grading , which is presumed to have taken place during the withdrawal of the ice front , when melting released vast amounts of water . the evidence for this lies in the occurrence of glacial sands and gravels , as well as glacial clays , which are sometimes laminated . throughout the region there are isolated basin sites which are thought to be remnants of old glacial lakes where water was trapped through the haphazard deposition of glacial debris . many of these have since been filled by peat which presumably developed in Atlantic and Sub-Atlantic times . brown earths in Britain . for many years in Britain the brown earth group has been divided into high and low base status soils ; the sub-division has been arbitrarily made , and in some cases a pH of 6.5 in the B horizon has been accepted as a line of division . since soils within the brown earth group , apart from limed soils and those marginal in affinity to calcareous soils , rarely have a pH of 6.5 in the B horizon the system is not perfect . when examining agricultural soils great confusion can result , for soils which are of low base status under semi-natural conditions can be induced to maintain the chemistry of high base status soils by liming and fertilizing . in parts of western Europe and eastern United States of America , where pedologists are concerned with soils in similar environments to Britain , two main sub-divisions of soils similar to our brown earths are recognised ( 1 ) acid soils with textural B horizons , i.e , with B horizons at least partly formed by illuviated clay , ( in western Europe Sol brun lessiv&amp;eacute; and Sol lessiv&amp;eacute; ; in U.S.A grey-brown podzolic soil ) : ( 2 ) strongly acid soils without textural B horizons , ( Sol brun acide , western Europe and U.S.A ) . obviously many more characteristics are required to define these sub-divisions , but these will be considered later . in Britain , on soil maps of our country we have used both grey-brown podzolic soil and sol brun acide as descriptive terms for particular areas . however , since in the west midlands , soils with textural B horizons are less well developed than typical grey-brown podzolic soils , advantage has been taken of the units used in western Europe . here well developed soils with moder humus and textural B horizons are called sol lessiv&amp;eacute; and less well developed soils with mull humus , sol brun lessiv&amp;eacute; ; thus , the latter unit , can be properly used to describe soils in the midlands . &amp;formula; . soil development . it is possible to extract two important groups from the variety of soils which occur on the drift deposits of the Cheshire-Shropshire plain , and these can be used to illustrate the type of soil formation characteristic of the region . the two groups of soils exemplify relationships within an extremely complex region . ( 1 ) . sols bruns acides and podzolised soils associated with glacial sands and gravels . ( 2 ) . sols bruns lessiv&amp;eacute;s and surface-water gley soils associated with glacial clays . ( 1 ) . sols bruns acides and podzolised soils . the glacial sands are highly siliceous , base poor parent materials , generally with less than 10 per cent clay , and most frequently with less than 5 per cent clay . the acid soils which have developed support a semi-natural cover of heath , or of deciduous wood-land consisting of oak and birch with some rowan and holly , and a bracken or heathy type of ground flora . under deciduous forest the humus form is moder , with F and H layers of approximately equal thickness , and under heath the humus form is frequently difficult to assess due to periodic burning . beneath these humus layers several types of profile may be found , but frequently the solum is freely drained , and shows little sign of development , being uniformly brown in colour apart from a slight colour ( B ) horizon - this typifies the sol brun acide . in detail it is a strongly desaturated soil throughout , with single grain or weak crumb structures , or in more loamy materials very weak fine sub-angular blocky structures . there is no texture profile ; estimates for free iron do not indicate any iron B horizon , and clay ratios do not show any significant differentiation of silica and sesquioxide . the sol brun acide is frequently associated in the landscape with soils showing signs of podzolisation , i.e , with soils having iron and/or humus B horizons , and these may be found in different stages of development . the course of soil development appears to be sol brun acide &amp;symbol; podzolised sol brun acide &amp;symbol; humus-iron podzol &amp;symbol; humus podzol ( fig 25 ) . a series of profiles examined at Delamere , north Cheshire , on glacial sands illustrates part of the development sequence ( fig 26 ) . extensive areas in Delamere were planted with oak early in the 19th century , and more or less cleared in the early years of the first world war . replanting consisted mainly of pine , though some open , degenerate , dry oak-birch woodland remains . the landscape unit drawn diagrammatically ( fig 26 ) is common on the Cheshire-Shropshire plain , and illustrates the gentle rolling relief , with a peat-filled basin . the podzolised sol brun acide has the following characteristics : 1 . thin moder , sharply separated from the mineral soil . 2 . some superficial bleaching immediately below the organic layer . 3 . an Ae horizon of approximately 9 ins of dark yellowish brown ( 10YR3/4 ) sand in which there are numerous bleached sand grains . 4 . a Bs horizon of 3/4 ins indicated by the yellowish red ( 5YR5/6 ) colour . hydrogen peroxide treatment of samples from the mineral horizons showed , when the organic matter was removed , that there is a well developed grey Ae horizon which gradually merges into the Bs horizon . the humus-iron podzol is considered to be a more mature profile for the Ae horizon is grey having lost most of its organic matter , and this is represented in a thin black horizon ( Bh ) overlying a strongly developed Bs horizon ( figs 25 and 26 ) . an ashy coloured residue is left after hydrogen peroxide treatment of the humus B horizon and this qualitatively suggests that it is low in inorganic iron ; however , chemical evidence from similar profiles indicates that a considerable amount of iron may be combined with organic matter in this layer , and this will be taken into solution by the hydrogen peroxide treatment . in the lowest position of the catena is the humus podzol ( figs 25 and 26 ) . it has the following characteristics : ( 1 ) . the humus form is transitional between mor and moder , though there is a marked pine needle litter . ( 2 ) . strongly bleached , deep Ae horizon , though it is traversed by a complex series of flow bands of colloidal organic matter . ( 3 ) . a thick ( 6 ins ) cemented black Bh horizon . ( 4 ) . there is no orange-brown Bs horizon ; the sub-soil consists of bleached sand , though here it is apparently affected by gleying . after hydrogen peroxide treatment of the horizons all are left completely bleached , confirming therefore , that there is no zone of iron accumulation within the profile . what are the factors which have operated in the differentiation of these soils ? since climate has had an overall influence , and all the profiles are developed on glacial sands and gravels , it may be assumed that differentiation is chiefly due to site and/or vegetation , or to vegetation as it is affected by man . it is widely believed that podzolisation in lowland Britain is the result of the dominant role which heath ( Calluna ) assumes in the vegetation cover of deforested or abandoned land . from this accepted doctrine , however , there is a real tendency to believe that all podzols are formed under heath ; to see a podzol is to point to the role of heath , on the site now , or in the past . work in western Europe in the last decade , and some confirmatory investigations in Britain , show podzolisation as a progressive development , starting under deciduous woodland and probably reaching maturity at the humus-iron podzol stage under Calluna , though in some cases heath may not be an essential part of the vegetation cycle . the occurrence of podzolised sols bruns acides and podzols in close proximity at Delamere and elsewhere , is difficult to explain in terms of past vegetation without a pollen analysis of the profiles concerned . there are so many possibilities in the thousands of years in which vegetation has influenced soil development . in the case of the humus podzols which are found in general adjoining peat or certainly in the lowest position in the catena , it can be convincingly argued that development has been influenced by ground-water . the presence of ground-water has prevented the precipitation of the illuviated iron oxides , or due perhaps to a change in regional or local water levels , formed iron B horizons have been disrupted by waterlogging and gleying ; in either case the leaching of humus is not confined by the filtering effect of an iron B horizon and consequently a more deeply leached profile results . 