Drainage tunnel in unstable ground, Tecklenburg, Germany, 1819.

Engraving by Le Blanc showing the method of contruction of underground tunnels using wooden beams. Illustration from 'De la richese minerale: Considerations sur les mines, usines et salines des differens etats, presentees comparativement' by Antoine-Marie Heron de Villefose (1774-1852), published in Paris in 1819. In English, the title is 'Of mineral riches: Considerations on the mines, factories and salt-mines of different countries, presented comparatively'.