Large-scale geophysical reconstruction of man-made ground at former industrial iron-furnace plantations

Abstract

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 (ERT), and electromagnetic (EM31) 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 (1) the distribution of remaining original soils could be mapped; (2) waste materials (e.g., slag, used brick, burned charcoal, iron ore, and broken-up sandstone or limestone) 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 (3) 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 (raceway) and a supply road). We conclude that geophysical techniques can play a key role in reconstructing man-made ground at former industrial furnace sites in North America.