(from the article `tunnels and underground excavations`) ...ancient practice of hand mining is still economical for some conditions (shorter and smaller tunnels) and may illustrate particular techniques ... Found on http://www.britannica.com/eb/a-z/f/46
(from the article `tunnels and underground excavations`) ...ancient practice of hand mining is still economical for some conditions (shorter and smaller tunnels) and may illustrate particular techniques ...