Saw this no where near 18th or 19th habitation. About 16in perfect circle, high ground, maybe 200 yrs from river. Second shallower one on same rock. Any ideas?
Such stones are also available here. Often they were inclusions of sandstone that have weathered. But there are also artificially made near prehistoric settlements. According to some sources, they were used as grain mills.
Thanks, Menzi. I read that they could be naturally made but they'd have to be in rivers like the picture you shared. The one I saw was nowhere near the river.
I'm not sure but I think the picture doesn't show a riverbed but holes filled by rain. Look at the link above. There are also some in the forest. From my experience I know similar holes from the Alps.