Very curious.
I think the map is correct in it's positioning of The Devil's Den and that the cromlech marked is now probably lost to us.
The barn you speak of, Moth, you encounter *before* you get to The Devil's Den (if walking up from the main road) and I don't recall a barn further up the valley.
Given the trashing of the Devil's Den during the 20th century (remember those big old rocks just by the footpath as you enter the field were once part of the monument and were quite recently cleared there), I think the cromlech has been pulled down. It would be interesting to see a map from around 1880 (to see if it was still there at the end of the 19th century) or more particularly the 1920/30s with the advent of motor driven farm machinery. A cromlech in the middle of field would be an irritant to plough around in one's new tractor, wouldn't it? And if you had a tractor you could more easily pull it down anyway.
Just my twopen'orth
J
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