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Figure 9: Raw fluxgate gradiometer data over a 20m by 20m area at Timberholme showing a square structure. Clipped range -150nT (white) to 150nT (black) The interpretation of the gradiometer data is shown on Figure 12. The leat (A) traverses the site and at its western end (B) turns sharply south and runs into the River Seph. A large area of slag (C) lies between the river and the leat. A square structure covering an area of about 10m by 10m (G) with an outer wall (D) is located on the north side of the leat. This structure is interpreted as a furnace site. The detailed earth resistance survey across it confirms the gradiometer results (Figure 10). The structure surrounding the furnace appears to continue southward to the river and may have been used to divert the leat water back into the river. Two areas of high gradiometer readings (E) positioned immediately south of the furnace could represent the remains of the demolished furnace, bridging or infilling the leat. North of the leat, two linear anomalies (J and K) stop short of it. The leat also cuts through a trapezoid-shaped anomaly (F) which could either be the

Figure 9 Raw fluxgate gradiometer data over a 20m by 20m area at Timberholme showing a square structure. Clipped range -150nT (white) to 150nT (black) The interpretation of the gradiometer data is shown on Figure 12. The leat (A) traverses the site and at its western end (B) turns sharply south and runs into the River Seph. A large area of slag (C) lies between the river and the leat. A square structure covering an area of about 10m by 10m (G) with an outer wall (D) is located on the north side of the leat. This structure is interpreted as a furnace site. The detailed earth resistance survey across it confirms the gradiometer results (Figure 10). The structure surrounding the furnace appears to continue southward to the river and may have been used to divert the leat water back into the river. Two areas of high gradiometer readings (E) positioned immediately south of the furnace could represent the remains of the demolished furnace, bridging or infilling the leat. North of the leat, two linear anomalies (J and K) stop short of it. The leat also cuts through a trapezoid-shaped anomaly (F) which could either be the

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In Wales, P Crew has been systematically excavating iron- working sites in Snowdonia since the 1970s (Crew and Crew 1997). Crew has also employed geophysical techniques on various sites dating from late prehistoric to 14th century. One of the first sites to be surveyed was Bryn y Castell, near Ffestiniog. A proton magnetometer survey defined the spread of metallurgical debris (P Crew pers comm). However the magnetometer data from Snow- donian iron-working sites can be affected by responses produced by the underlying igneous and metamorphic rocks. Consequently magnetic susceptibility surveying, a technique that is not generally affected by the geological background conditions as it only responds to shallow anomalies, has tended to supersede magnetometer work on some sites. At Crawcwellt West, near Traws-fynydd, for example, a magnetic susceptibility survey was successfully correlated with the distribution of slag across the site (Crew 1990). possible Roman ‘iron roasting hearth’ was located (Jones and Shotter 1988). Neither account records detailed survey information, but investigation by R W Vernon has revealed that the former survey consisted of two traverses centred on a positive magnetic anomaly.
In Wales, P Crew has been systematically excavating iron- working sites in Snowdonia since the 1970s (Crew and Crew 1997). Crew has also employed geophysical techniques on various sites dating from late prehistoric to 14th century. One of the first sites to be surveyed was Bryn y Castell, near Ffestiniog. A proton magnetometer survey defined the spread of metallurgical debris (P Crew pers comm). However the magnetometer data from Snow- donian iron-working sites can be affected by responses produced by the underlying igneous and metamorphic rocks. Consequently magnetic susceptibility surveying, a technique that is not generally affected by the geological background conditions as it only responds to shallow anomalies, has tended to supersede magnetometer work on some sites. At Crawcwellt West, near Traws-fynydd, for example, a magnetic susceptibility survey was successfully correlated with the distribution of slag across the site (Crew 1990). possible Roman ‘iron roasting hearth’ was located (Jones and Shotter 1988). Neither account records detailed survey information, but investigation by R W Vernon has revealed that the former survey consisted of two traverses centred on a positive magnetic anomaly.
The three geophysically surveyed sites have now become part of a much larger project to investigate the iron- working industry of the North Yorkshire Moors. The area is considered to have a number of advantages which makes the application of geophysics worthwhile. The area has: was referred to as Smiddesdal(e) (Smiths’ Dale), a name of Nordic origin (McDonnell 1963). About 1170, a ferrarius (ironsmith) was operating north of Laskill for Stainton, now a lost village (McDonnell 1972). It was also during the 12th century, that the Cistercian order started to establish granges (Pratt 1969), outlying settlements, to administer or farm the more remote portions of the Abbey lands. Such communities could specialise in iron-working activities as part of their day to day operations (McDonnell 1963). The surveyed Grange site had been such an
The three geophysically surveyed sites have now become part of a much larger project to investigate the iron- working industry of the North Yorkshire Moors. The area is considered to have a number of advantages which makes the application of geophysics worthwhile. The area has: was referred to as Smiddesdal(e) (Smiths’ Dale), a name of Nordic origin (McDonnell 1963). About 1170, a ferrarius (ironsmith) was operating north of Laskill for Stainton, now a lost village (McDonnell 1972). It was also during the 12th century, that the Cistercian order started to establish granges (Pratt 1969), outlying settlements, to administer or farm the more remote portions of the Abbey lands. Such communities could specialise in iron-working activities as part of their day to day operations (McDonnell 1963). The surveyed Grange site had been such an
Figure 4: The Grange showing the fluxgate gradiometer survey grid superimposed on the surface contours. The magnetic susceptibili surveys were conducted in Areas I and 2
Figure 4: The Grange showing the fluxgate gradiometer survey grid superimposed on the surface contours. The magnetic susceptibili surveys were conducted in Areas I and 2
Figure 6: Interpretation of the fluxgate gradiometer data foi The Grange fulfilled several of the objectives. The extent of the iron working activity has been delineated and associated features have been identified. The relationships of these features also demonstrate that iron-working was an integrated function with other on-site activity.
Figure 6: Interpretation of the fluxgate gradiometer data foi The Grange fulfilled several of the objectives. The extent of the iron working activity has been delineated and associated features have been identified. The relationships of these features also demonstrate that iron-working was an integrated function with other on-site activity.
Figure 13: Topographical survey of the site at Forge Farm
Figure 13: Topographical survey of the site at Forge Farm
was more than one phase to the site development. This is corroborated by evidence from the magnetic susceptibility values obtained from slag samples which is discussed in a later section.
was more than one phase to the site development. This is corroborated by evidence from the magnetic susceptibility values obtained from slag samples which is discussed in a later section.
Figure 14: Raw fluxgate gradiometer data from Forge Farm. Clipped range -260nT (white) to 234nT (black) Figure 16: Raw magnetic susceptibility data from Forge Farm Clipped range 50 x 10° (SI) (white) to 800 x 10° (SI) (black)
Figure 14: Raw fluxgate gradiometer data from Forge Farm. Clipped range -260nT (white) to 234nT (black) Figure 16: Raw magnetic susceptibility data from Forge Farm Clipped range 50 x 10° (SI) (white) to 800 x 10° (SI) (black)
Figure 15: Raw earth resistance data from Forge Farm. Clippec range 300 ohms (white) to 520 ohms (black)
Figure 15: Raw earth resistance data from Forge Farm. Clippec range 300 ohms (white) to 520 ohms (black)
Table 2: Chemical analyses of two of the main Jurassic ironstone horizons (after Percy 1864)
Table 2: Chemical analyses of two of the main Jurassic ironstone horizons (after Percy 1864)
Table 1: Comparison of the chemical analyses of slags with their magnetic susceptibility value.
Table 1: Comparison of the chemical analyses of slags with their magnetic susceptibility value.
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Archaeological Geophysics
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