I managed to find another of the Sheffield seam outcrops the other day, after much furtling in the undergrowth. This is the Whinmoor, or Mickley Thick seam, just updip from the Silkstone seam, a much more famous (and larger) one. It cuts through Gleadless, Arburthorne and Norfolk Park, before heading into the town centre - there's not a lot visible these days, and this will vanish in a month once the vegetation has grown back. But it's a good example of how these seams were originally discovered. I did bring a bit home with me, but not much your honour, only a pocketful.