What are these stones?

My lathe is set up opposite what looks to me to be a charcoal pit, but I’m informed that it’s a chop wood kiln. Basically it’s a 6 foot wide, stone lined bowl shaped depression. Anyway, it’s something to do with working the woods no doubt as I found another one in a different section of the woods. Scattered around the one near my bodgery are eight pairs of rocks, which look to have been deliberately rolled together, and there is usually a smaller outlier. I wonder what these may have been used for. Some sort of primitive vice perhaps? They are pretty low – about 2 foot high at most, but they may have sunk a bit over the years. I’m thinking how I could use them (looks like a really good way to blunt an edge!)? Maybe they go back to when the wood was coppiced, which it hasn’t been for many years and the wood is now just continuous cover managed. Here’s a picture, outlier in foreground, two stones center further back:

Although there is still snow on the ground and frosty nights and mornings there are definite signs of Spring: Long Tailed Tits in pairs rather than flocking; sprouting Garlic now as well as Bluebells which have been around for some weeks; warblers singing.