In mining and geology, the rock formation that lies directly below a sloping fault or vein of ore.
Geological term: 'foot' + 'wall' (rock formation). Emerged in 19th-century mining terminology to describe the lower surface of tilted mineral deposits, contrasting with the 'hanging wall' above.
Miners had to mentally flip their thinking—the 'footwall' is actually above the 'hanging wall' in terms of gravity, because these names describe the miner's position relative to the fault, not actual location!
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