text: I’m not sure if I’ll get a chance to go there and resurvey. From my trip along the Frosterley Cut today, there are plenty more markers up there.
  
  From some reading about the railway, these seem to be boundary markers rather than (as I’d assumed) milestones. The railway land was leased, rather than purchased, so they might be to mark the extent of the leased area. There are loads of them near the Frosterley Cut, on both sides of the railway corridor.