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The value of geophysical methods in investigating iron furnaces in North America (of which several hundred exist) has so far been poorlyevaluated.We report on the magnetic gradiometerandelectrical resistivity surveys conducted at the Shade iron furnace, Pennsylvania, USA, together with results fromground-truthingexcavations.We findthat (i) numeroususefuldata sets couldberecordeddespite challenging field conditions; (ii) reconnaissance gradiometerandresistivitydatayield complementary informationallowinglarge-scale sitereconstruction; (iii) high-resolutionresistivitydatareflect archaeologically valuable site lithologies with decimetre-scale accuracy; and (iv) extreme absolute background values (several hundred nT) of, and spatial contrasts (several hundred to >1000 nT) in, the gradiometer data are common owing to the presence of much burnt material and iron artefacts. We conclude that geophysical investigations of iron furnaces in North America may yield spatially extensive subsurface information of substantial archaeological value, which is impossible to obtain using traditional archaeological survey methods alone

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Blast-iron-furnace plantations were widespread throughout colonial and postcolonial America and therefore represent sites of specific archaeological interest. Because such plantations often were a really extensive, historical reconstruction of a site is challenging using conventional archaeological field techniques alone. Therefore, we appraise the usefulness of integrating magnetic gradiometer, electrical-resistivity tomography ͑ERT͒, and electromagnetic ͑EM31͒ data in detecting and delineating buried structures related to former operation of the Shade furnace, a typical industrial plantation in 19th-century Pennsylvania. The geophysical results were ground-truthed in seven locations by archaeological excavation. Geophysical results demonstrated that ͑1͒ the distribution of remaining original soils could be mapped; ͑2͒ waste materials ͑e.g., slag, used brick, burned charcoal, iron ore, and broken-up sandstone or limestone͒ within or above the original soils could be detected and delineated, whether the material occurred in pits or lenses or was dispersed across the ground surface; and ͑3͒ the location and spatial extent of many former structures related to furnace operation could be identified, such as building or bridge foundations and casting-related structures ͑e.g., the tapping channel or the casting floor, and the former courses of a water canal ͑raceway͒ and a supply road͒. We conclude that geophysical techniques can play a key role in reconstructing man-made ground at former industrial furnace sites in North America.