Aye, I know what they are. They used to collapse on the Town Moor and get fenced off and filled in - then the council decided to get serious and stripmined the lot. That's why Newcastle's here; it's built on coal. But there are no bell pits on Smithills Moor, nor on Knarsdale Fell. The first has adits, the second sinkholes (and adits). Both got megaliths too. See what you mean about fairy rings forming part circles but you'll have to find a pretty good link to show that they can grow to 50 - 80 metres in diameter. I would have seen one by now, probably. Great year for fungi though !