The book that I am preparing on the history of the mines at Matlock in Derbyshire mentions a couple of incidents illustrating the difficulty of transporting heavy mining loads. The 12 ton boiler being transported to Cawdor Mine in 1853 ran over and killed a child, and then after delivery, the massive drug (wagon) ran over and seriously injured a workman.
More recently, when a 3 ton boiler was being taken along the rough track to High Loft Mine then being worked for fluorspar on top of Masson Hill in October 1923, several of the six horses pulling the waggon fell down. The load had to be cut free to prevent them all being dragged headlong down the precipice. The massive boiler then began rolling towards the cliff, threatening disaster, but it soon came to rest, having caused only slight damage. If the boiler had rolled unchecked down the hillside, it could have gone all the way down to the valley floor in Matlock Dale 700 feet below where there were houses and a busy road.