STANLEY GRANGE, WEST HALLAM, DERBYSHIRE Topsoil Magnetic Susceptibility and Gradiometer Survey ( Survey Ref : 1080397/STD/RJB ) APRIL 1997 Produced by OXFORD ARCHAEOTECHNICS LIMITED under the direction of A.E. Johnson BA(Hons) Commissioned by Trent & Peak Archaeological Trust on behalf of RJB Mining (UK) Limited OXFORD ARCHAEOTECHNICS Specialist Archaeological Field Evaluation OXFORD ARCHAEOTECHNICS Noke Oxford OX3 9TX Tel / Fax 01865 375536 Mobile 07831 383295 Email: archaeotechnics@gmail.com http://www.archaeotechnics.co.uk CONTENTS SUMMARY 1 1. INTRODUCTION 2 2. MAGNETIC SURVEY DESIGN 3 3. SURVEY RESULTS Topsoil Magnetic Susceptibility Survey Magnetometer (gradiometer) survey 5 5 7 4. CONCLUSIONS 11 REFERENCES 12 APPENDIX: Magnetic Techniques - General Principles 13 FIGURES SUMMARY A geophysical evaluation programme comprising topsoil magnetic susceptibility mapping and gradiometer survey was carried out on an 8.57 ha area of land adjacent to Stanley Grange Farm, West Hallam, Derbyshire (centred on NGR 442700 340650), in advance of proposed open cast coal mining. The survey was based upon the principle that past human activity and its associated debris usually creates slight but persistent changes in the local magnetic environment which can be sensed from the surface (using magnetic susceptibility measurement and magnetometry). 10 m magnetic susceptibility survey located several areas showing extremely enhanced topsoils suggesting dispersed local burning events. Detailed gridded magnetometer (gradiometer) survey confirmed the presence of numerous probable industrial features within these zones. A single auger hole into one of these intrusive features confirmed the presence of burnt clay and charcoal; the combined evidence of previous fieldwalking (?metalworking slag and pottery) with the geophysical survey indicates an ironworking site of possible Medieval date. Two further isolated outlying features were also identified by gradiometer scanning. 1. INTRODUCTION 1.1 Geophysical survey was commissioned by Trent & Peak Archaeological Trust on behalf of RJB Mining (UK) Ltd. on land adjacent to Stanley Grange Farm, West Hallam, Derbyshire in advance of proposed open cast coal mining. The fieldwork was carried out in March 1997. 1.2 The survey area (centred at NGR 442700 340650) comprises an L-shaped area of farmland in three fields 8.57 ha in extent (OS Fields 6871, 8053 & part of 6654), bounded on the north by Station Road, on the east by Cat and Fiddle Lane, and on the west partly by the farm access track and open fields, and extending southwards as far as the Stanley Brook. A hedgeline running across the extreme northwest angle of the survey area marks the parish boundary between Stanley and West Hallam. The location is shown on Fig. 1. 1.3 The solid geology is recorded as Carboniferous Coal Measures. There are some superficial alluvial deposits, notably on the southern boundary of the survey area adjacent to the brook. 1.4 Previous fieldwalking by Trent & Peak Archaeological Trust had identified concentrations of Medieval pottery sherds together with ?metalworking slag extending over an area some 100 x 60 m within the centre/south of the northernmost survey field (centred on NGR 442660 340660). 1.5 The geophysical survey comprised a combination of topsoil magnetic susceptibility field sensing and magnetometry. An explanation of the techniques used, and the rationale behind their selection, is included in an Appendix to the present report. 2 2. MAGNETIC SURVEY DESIGN 2.1 Survey control was established to the National Grid by EDM Total Station. 2.2 The equipment used for the direct topsoil magnetic susceptibility survey was a Bartington Instruments MS2 meter with an 18.5 cm loop. 2.3 In situ magnetic susceptibility readings were taken on a 10 m grid, an interval known to give a high probability of intersecting with dispersed horizons from a wide range of archaeological sites, particularly those associated with occupation and industrial activity from the later prehistoric period onwards. Soils over former occupation and industrial sites usually register as stronger patterning, frequently showing a marked focus. Agricultural activity helps to both generate (by ploughing casting up underlying deposits), and ultimately disperses the more magnetic soils over a wider area. Patterns recorded by 10 m magnetic susceptibility mapping tend to define zones of former activity rather than locate individual elements. Nevertheless, in some contexts, a focus of markedly stronger soil magnetic susceptibility (or markedly magnetically lower soils indicative of ploughed down earthworks) is occasionally found to relate to material dispersed from specific underlying features. 2.4 Routine scanning by gradiometer was undertaken at 25 m traverse intervals to check for any major concentrations of underlying archaeological features whose presence may not have been detected by the topsoil susceptibility survey. Five areas (totalling 1.53 ha) showing significant enhanced topsoil magnetic susceptibility and/or gradiometer scanning anomalies were targeted for detailed gridded gradiometer survey with a Geoscan Research FM 36 Fluxgate Gradiometer (sampling 4 readings per metre at 1 metre traverse 3 intervals in the 0.1 nT range). The nanotesla (nT) is the standard unit of magnetic flux (expressed as the current density), here used to indicate positive and negative deviations from the Earth's normal magnetic field. 2.5 The topsoil magnetic susceptibility colour shade plot (Fig. 2) shows contours at a selected range of SI intervals. Magnetometer data have been presented as grey scale raw data and stacked trace plots (Figs. 3,6 7 & 8); an interpretation of results is shown on Fig. 4 and an overview in relation to topsoil magnetic susceptibility in Fig. 5. 4 3. SURVEY RESULTS TOPSOIL MAGNETIC SUSCEPTIBILITY SURVEY 3.1 A total of 857 in situ magnetic susceptibility readings was recorded. Susceptibility is reported in SI:volume susceptibility units (x 10-5), a dimensionless measure of the relative ease with which a sample can be magnetized in a given magnetic field. 3.2 In situ topsoil susceptibility measurements at Stanley Grange display an exceptional dynamic range between 4 and 3050 (x 10-5) SI units. The mean for the survey was 125 SI units and the standard deviation calculated against the mean was 289 SI units, although these values are influenced strongly by extreme local variations in the vicinity of what appear to be former industrial activity areas. 3.3 The response of topsoil magnetic susceptibility survey is essentially to enhanced material within the topsoil, and is most likely to be due to the presence of relatively fine-grained material, especially dispersed burnt clays; care was taken as far as practicable to discriminate between the logging of readings from obvious ferrous material or slag which, although locally present was not so abundant as to hamper topsoil magnetic susceptibility mapping. 3.4 Several foci of strongly enhanced topsoils were mapped within OS Field 6871. The principal focus covers an area some 100 x 70 m (centred on NGR 442680 340660), with topsoils exceeding 200 SI (containing two point foci of 3,050 and 2747 SI). A second smaller focus (c.50 x 25 m) (exceeding 200 SI and reaching 524 SI) lies some 70 m to the northwest (centred on NGR 442615 5 340755). These two foci are joined by a narrow strip of magnetically enhanced topsoils on a northwest-southeast trend. A third focus lies 50 m west of the principal zone of enhancement (centred on NGR 442600 340650), covering an area of c.50 x 30 m, with topsoils locally exceeding 1666 SI. At least three further small pockets of enhancement were recorded to the west and southwest of this location (centred on NGR 442585 340605, 442575 340675 & 442538 340620). 3.5 Apart from these strongly enhanced zones, the topsoil magnetic susceptibility map also shows patterns of existing and former land divisions. The band of low magnetic susceptibility recorded between the principal and western foci of enhancement may indicate the position of a former land boundary. 3.6 Further patterns consistent with the current agricultural regime and existing hedgerows are also apparent, with the majority of both stronger and weaker patterning exhibiting a northwest-southeast trend. These patterns represent at least the last two centuries of cultivation (recently felled trees along the eastwest hedgerow are at least 200 years old). 3.7 Both fields lying south of the main magnetic focus (OS Fields 6654 & 8053) show relatively low susceptibility levels; the slight contrasts recorded between the western pasture field and the neighbouring arable field reflect the differences in landuse, the latter having been ploughed recently during ploughing competitions, but both generally display the weaker magnetic characteristics of long-term pasture. There may be some alluvial cover towards the southernmost boundaries of these fields which might possibly mask underlying archaeological horizons. 6 MAGNETOMETER (GRADIOMETER) SURVEY 3.8 The survey area was scanned by gradiometer on 25 m traverses. Scanning over the stronger topsoil magnetic susceptibility patterns rapidly confirmed the presence of extremely strong magnetic anomalies. Gridded gradiometer survey was carried out in five areas, two of which showed strongly enhanced topsoil magnetic susceptibility together with two small areas selected to investigate gradiometer scanning anomalies, and the fifth close to the Stanley Brook, where a quantity of iron slag was visible on the stream bank. A total area of 1.53 ha was investigated by detailed gradiometer grids, their location is shown on Fig. 1. The relationship between the topsoil magnetic susceptibility map and areas surveyed by detailed gradiometry are shown on Fig. 3. AREA 1 (Figs. 3 & 6) 3.9 An irregularly shaped 1 ha gradiometer survey area (maximum dimensions: 150 x 90 m) was sited to investigate the three main foci of magnetic enhancement recorded during topsoil magnetic susceptibility mapping (gradiometer scanning had confirmed strong patterns of underlying intrusive features, together with what appears to be pockets of ferrous/slag material at all three locations). 3.10 Magnetic anomalies within each of the defined areas are so strong that they tend to mask any subtle geometry, and there may be superimposition of burnt features within these locations. 3.11 The major concentrations of activity are defined by stronger broken red outlines on Fig. 4, whereas outlying features, provisionally described as pits 7 (which may however include discrete burnt structures such as furnace bases) are outlined in thinner broken red lines. 3.12 A single hand auger hole (NGR 442695 340640) demonstrated an underlying intrusive feature containing burnt clay and charcoal extending at least 1 m below the present ground surface. 3.13 There are numerous northwest - southeast striations (both positive and negative anomalies) crossing the core of the survey block which are the result of agricultural activity ‘dragging’ contrasting magnetic soils along the lines of cultivation. A second weaker subset of multiple striations which lies almost perpendicular, on a roughly northeast-southwest trend, must represent a previous (albeit relatively modern) cultivation pattern. AREA 2 (Figs. 3 & 7) 3.14 This 30 x 30 m (0.09 ha) grid was surveyed to investigate an isolated gradiometer scanning anomaly. The gradiometer plot shows a feature which is provisionally interpreted as a pit some 1.5 m in diameter, although the magnetic response suggests either that a quantity of burnt material has been incorporated into a pitfill, or that the feature represented is an isolated fired structure. AREA 3 (Figs. 3 & 7) 3.15 This 60 x 30 m (0.18 ha) survey grid was sited to investigate a small focus of topsoil magnetic enhancement lying 100 m northwest of the principal focus investigated in Area 1. 8 3.16 A pit-like anomaly was recorded (perhaps a pit or a burnt structure some 1.5 2 m in diameter) which probably accounts for the focus of topsoil enhancement. 3.17 Multiple agricultural marks visible on a northwest-southeast alignment represent a continuation of similar marks noted in Area 1 (above); agricultural activity may adequately explain the apparent ‘corridor’ of raised magnetic susceptibility linking Areas 1 and 3. AREA 4 (Figs. 3 & 8) 3.18 A 30 x 30 m (0.09 ha) survey grid was sited to investigate a gradiometer scanning anomaly lying almost 100 m southeast of the principal magnetic focus investigated in Area 1, close to the hedgerow dividing the two southern fields (OS 6654 & 8053). 3.19 This is an area of magnetic activity located by gradiometer scanning which otherwise displays no associated topsoil magnetic susceptibility enhancement and is therefore unlikely to be of a similar nature (burnt) to those anomalies recorded in Areas 1, 2 or 3. The numerous ‘iron spikes’ recorded on the gradiometer plot suggest that the area includes local incorporation of ferrous material into the soil extending over an area of some 10 x 8 m. It is probable that these signals represent hollows or pits containing (?recent) ferrous or other debris. 3.20 One possible small pit c.1 m in diameter lies centrally close to the northern boundary of the survey grid. 9 AREA 5 (Figs. 3 & 8) 3.21 A 30 x 30 m (0.09 ha) survey area was sited close to the stream bank on the southern boundary of the survey area to investigate gradiometer scanning anomalies associated with weak topsoil magnetic susceptibility patterning. Close observation of the eroded stream bank at this location revealed isolated pieces of tap slag exposed at a depth of almost 1 m beneath the present ground surface, and a mounded area visible on the opposite bank appears to comprise quantities of similar material. 3.22 The relatively subtle response of the gradiometer to features in this area suggests the possibility of alluvial or colluvial masking of potential archaeological horizons lying at a greater depth than recorded elsewhere within the survey. 3.23 An area measuring approximately 10 x 5 m within the southwest corner of the gradiometer survey block suggests the presence either of more deeply buried features or an horizon of industrial material/debris. 3.24 There are weak indications of intrusive lineations or grouped pits lying central to the survey grid on a northwest - southeast alignment, covering an area some 12 - 15 m in length. The elements are relatively narrow (perhaps less than 1 m), and again more deeply buried features may be represented. 3.25 A group of three lineations extending from the survey area at roughly 4 - 5 m centres (shown as broken blue lines on Fig. 4) may be either agricultural striations or drainage features. 10 4. CONCLUSIONS 4.1 The combination of topsoil magnetic susceptibility mapping and gradiometer survey has produced dynamic plots which clearly indicate the presence of a number of intensely burnt features, principally within the core of the survey area (centre/south of OS Field 6871), although further outlying activity close to the modern stream bank may also be suspected. 4.2 Both the range of topsoil magnetic susceptibility and strength of gradiometer anomalies suggest a fairly extensive industrial site which is most likely, judging from surface finds of iron slag, to be associated with ironworking and on the basis of surface finds assignable to a possible Medieval date. 4.3 There is no doubt that at a number of locations a reasonable depth of burnt deposits is present. A single hand auger hole demonstrated an underlying intrusive feature containing burnt clay and charcoal extending at least 1 m below the present ground surface. There is, however, some suspicion of truncation of archaeological horizons, as agricultural activity has dispersed underlying burnt material into the ploughsoil over a considerable area. 4.4 Both topsoil magnetic susceptibility mapping and gradiometer survey appear to have located the principal zones of activity, which include numerous burning episodes, although it is not inconceivable that other activity or outlying structures may be present which have not been differentiated against a background of extremely strong magnetic signals. 11 REFERENCES CLARK, A.J. 1990. Seeing Beneath the Soil. B.T. Batsford Ltd: London. GALE, S.J. & HOARE, P.G. 1991. Quaternary Sediments: petrographic methods for the study of unlithified rocks. Belhaven Press: London (see Section 4.7, pp.201-229, "The magnetic susceptibility of regolith materials"). SCOLLAR, I., TABBAGH, A., HESSE, A. & HERZOG, I. 1990. Archaeological Prospecting and Remote Sensing. Cambridge University Press. THOMPSON, R. & OLDFIELD, F. 1986. Environmental Magnetism. Allen & Unwin: London. ACKNOWLEDGEMENTS Topsoil magnetic susceptibility mapping and magnetometer survey by Oxford Archaeotechnics Limited under the direction of A.E. Johnson BA(Hons), with: M. Ayers BSc(Hons), Msc and J. Porter BSc(Hons). 12 APPENDIX 1 - MAGNETIC TECHNIQUES: GENERAL PRINCIPLES A1.1 It is possible to define areas of human activity (particularly soils spread from occupation sites and the fills of cut features such as pits or ditches) by means of magnetic survey (Clark 1990; Scollar et al. 1990). The results will vary, according to the local geology and soils (Thompson & Oldfield 1986; Gale & Hoare 1991), as modified by past and present agricultural practices. Under favourable conditions, areas of suspected archaeological activity can be accurately located and targeted for further investigative work (if required) without the necessity for extensive random exploratory trenching. Magnetic survey has the added advantages of enabling large areas to be assessed relatively quickly, and is non-destructive. A1.2 Topsoil is normally more magnetic than the subsoil or bedrock from which it is derived. Human activity further locally enhances the magnetic properties of soils, and amplifies the contrast with the geological background. The main enhancement effect is the increase of magnetic susceptibility, by fire and, to a lesser extent, by the bacterial activity associated with rubbish decomposition; the introduction of materials such as fired clay and ceramics - and, of course, iron and many industrial residues - may also be important in some cases. Other agencies include the addition and redistribution of naturally magnetic rock such as basalt or ironstone, either locally derived or imported. 13 A1.3 The tendency of most human activity is to increase soil magnetic susceptibility locally. In some cases, however, features such as traces of former mounds or banks, or imported soil/subsoil or non-magnetic bedrock (such as most limestones), will show as zones of lower susceptibility in comparison with the surrounding topsoil. A1.4 Archaeologically magnetically enhanced soils are therefore a response of the parent geological material to a series of events which make up the total domestic, agricultural and industrial history of a site, usually over a prolonged period. Climatic factors may subsequently further modify the susceptibility of soils but, in the absence of strong chemical alteration (e.g. during the process of podzolisation or extreme reduction), magnetic characteristics may persist over millions of years. A1.5 Both the magnetic contrast between archaeological features and the subsoil into which they are dug, and the magnetic susceptibility of topsoil spreads associated with occupation horizons, can be measured in the field. A1.6 There are several highly sensitive instruments available which can be used to measure these magnetic variations. Some are capable, under favourable conditions, of producing extraordinarily detailed plots of subsurface features. The detection of these features is usually by means of a magnetometer (normally a fluxgate gradiometer). These are defined as passive instruments which respond to the magnetic anomalies produced by buried features in the presence of the Earth's magnetic field. The gradiometer uses two sensors mounted vertically, often 50 cm apart. The bottom sensor is carried some 30 cm above the ground, and registers local magnetic anomalies with respect to the top 14 sensor. As both sensors are affected equally by gross magnetic effects these are cancelled out. In order to produce good results, the magnetic susceptibility contrast between features and their surroundings must be reasonably high, thereby creating good local anomalies; a generally raised background, even if due to human occupation within a settlement context, will sometimes preclude meaningful magnetometer results. The sensitive nature of magnetometers makes them suitable for detailed work, logging measurements at a closely spaced (less than 1 metre) sample interval, particularly in areas where an archaeological site is already suspected. Magnetometers may also be used for rapid 'prospecting' (‘scanning’) of larger areas (where the operator directly monitors the changing magnetic field and pinpoints specific anomalies). A1.7 Magnetic susceptibility measuring systems, whilst responding to basically the same magnetic component in the soil, are 'active' instruments which subject the sample area being measured (according to the size of the sensor used) to a low intensity alternating magnetic field. Magnetically susceptible material within the influence of this field can be measured by means of changes which are induced in oscillator frequency. For general work, measuring topsoil susceptibility in situ, a sensor loop of around 20 cm diameter is convenient, and responds to the concentration of magnetic (especially ferrimagnetic) minerals mostly in the top 10 cm of the soil. Magnetically enhanced horizons which have been reached by the plough, and even those from which material has been transported by soil biological activity, can thus be recognised. 15 A1.8 Whilst only rarely encountering anomalies as graphically defined as those detected by magnetometers, magnetic susceptibility systems are ideal for detecting magnetic spreads and thin archaeological horizons not seen by magnetometers. Using a 10 m interval grid, large areas of landscape can be covered relatively quickly. The resulting plot can frequently determine the general pattern of activity and define the nuclei of any occupation or industrial areas. As the intervals between susceptibility readings generally exceed the parameters of most individual archaeological features (but not of the general spread of enhancement around features), the resulting plots should be used as a guide to areas of archaeological potential and to suggest the general form of major activity areas; further refinement is possible using a finer mesh grid or, more usually, by detailing underlying features using a gradiometer. A1.9 Magnetic survey is not successful on all geological and pedological substrates. As a rule of thumb, in the lowland zone of Britain, the more sandy/stony a deposit, the less magnetic material is likely to be present, so that a greater magnetic contrast in soil materials will be needed to locate archaeological features; in practice, this means that only stronger magnetic anomalies (e.g. larger accumulations of burnt material) will be visible, with weaker signals (e.g. from the fillings of simple agricultural ditches) disappearing into the background. Similar problems can arise when the natural background itself is very high or very variable (e.g. in the presence of sediments partially derived from magnetic volcanic rocks). A1.10 The precise physical and chemical processes of changing soil magnetism are extremely complex and subject to innumerable 16 variations. In general terms, however, there is no doubt that magnetic enhancement of soils by human activity provides valuable archaeological information. A1.11 As well as locating specific sites, topsoil magnetic susceptibility survey frequently provides information relating to former landuse. Variations in the soils and subsoils, both natural and those enhanced by anthropogenic agencies, when modified by agriculture, give rise to distinctive patterns of topsoil susceptibility. The containment of these spreads by either natural or man-made features (streams, hedgerows, etc.) gives rise to a characteristic chequerboard or strip pattern of varying enhancement, often showing the location of former field systems, which persist even after the physical barriers have been removed. These patterns are often further amplified in fields containing underlying archaeological features within reach of the plough. More subtle landuse boundaries and indications of former cultivation regimes are often suggested by topsoil magnetic susceptibility plots. A1.12 Where a general spread of magnetically enhanced soils contained within a long-established boundary becomes admixed over a long period by constant ploughing, it can be diffused to such a point that the original source is masked altogether. Magnetically enhanced material may also be moved or masked by natural agencies such as colluviation or alluviation. Generally, it appears that the longer a parcel of land has been under arable cultivation, the greater is the tendency for topsoil susceptibility to increase; at the same time there is increasing homogeneity of the magnetic signal within the soils owing to continuous agricultural mixing of the material. Some patterns of soil enhancement derived from underlying archaeological features are, 17 however, apparently capable of resisting agricultural dispersal for thousands of years (Clark 1990). 18 FIGURE CAPTIONS Figure 1. Location maps. Scale 1:50,000 and 1:5000. Based upon OS 1:50,000 Map 129, and reduced from OS 1:2500 Sheet SK 4240. Figure 2. Topsoil magnetic susceptibility survey: colour shade plot. Scale 1:2500. Figure 3. Gradiometer survey. Areas 1 - 5: grey shade plots (Geoscan Research Geoplot Licence No. GPB 885-6). Scale 1:1000. Figure 4. Gradiometer survey. Areas 1 - 5: interpretative plots (Geoscan Research Geoplot Licence No. GPB 885-6). Scale 1:1000. Figure 5. Gradiometer survey. Overview, showing gradiometer results in relation to topsoil magnetic susceptibility (Geoscan Research Geoplot Licence No. GPB 885-6). Scale 1:2500. Based upon OS 1:2500 Sheet SK 4240. Figure 6. Gradiometer survey. Area 1: stacked trace plot (raw data) (Geoscan Research Geoplot Licence No. GPB 885-6). Scale 1:1000. Figure 7. Gradiometer survey. Areas 2 & 3: stacked trace plot (raw data) (Geoscan Research Geoplot Licence No. GPB 885-6). Scale 1:1000. Figure 8. Gradiometer survey. Areas 4 & 5: stacked trace plots (raw data) (Geoscan Research Geoplot Licence No. GPB 885-6). Scale 1:1000. Ordnance Survey maps reproduced by Oxford Archaeotechnics, Licence No AL51636A0001, with the permission of the Controller of HMSO, Crown Copyright. 19 Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility & magnetometer survey: Location 340800 3 1:50,000 2 OS 6871 340700 1 340600 4 OS 6654 Topsoil magnetic susceptibility survey OS 8053 340500 5 Magnetometer (Gradiometer) survey 30m grids 1:5000 FIG. 1 Stanley Grange,West Hallam Derbyshire Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility, colour shade plot 340900 Topsoil magnetic susceptibility and magnetometer survey 340800 N 2000 1000 500 1:2500 340700 250 200 180 160 140 120 100 80 60 40 20 15 340600 10 5 340500 340400 OXFORD ARCHAEOTECHNICS FIG. 2 C O A Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility & magnetometer survey 5 Gradiometer grey shade plot 2 1 4 442700 442700 3 For interpretation see fig 4 1:1000 -15 -10 -5 0 5 10 15 20 25 nT FIG. 3 Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility & magnetometer survey 5 Gradiometer grey shade plot 2 1 4 442700 442700 3 Interpretation Linear and curvilinear features Positive anomaly Negative anomaly Areas of burning & disturbed ground. (including furnace material?) 1:1000 -15 -10 -5 0 5 10 15 20 25 nT Possible pits (mostly industrial/burnt) Weak linear and curvilinear features, including agricultural striations Ferrous material (main concentrations) FIG. 4 Stanley Grange, West Hallam, Derbyshire Magnetometer (Gradiometer) survey: Overview (in relation to topsoil magnetic susceptibility) 340800 Outlying burnt features 3 2 Focus of industrial activity ( iron smelting ?) 340700 OS 6871 1 340600 Structural debris (modern ?) 4 OS 6654 OS 8053 340500 5 Further iron slag present on streambank Topsoil magnetic susceptibility contours SI (x10 -5 ) Gradiometer survey, 30m grids 1:2500 FIG. 5 Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility & magnetometer survey Gradiometer stacked trace plot (raw data), area 1 442700 370 nT 1:1000 FIG. 6 Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility & magnetometer survey Gradiometer stacked trace plot (raw data) , areas 2 & 3 2 3 340730 370 nT 1:1000 FIG. 7 Stanley Grange, West Hallam, Derbyshire Topsoil magnetic susceptibility & magnetometer survey Gradiometer stacked trace plot (raw data), area 4 4 370 nT 1:1000 Gradiometer stacked trace plot (raw data), area 5 5 370 nT 1:1000 FIG. 8