Hmm, difficult to get a good angle on these - and they're spaced so far apart! Inconsiderate ancient folk!! Sigh.
There are three of them, the first two are obvious, the third is right at the left-hand-side between some trees.
There's a blokey walking his dog by the middle one for scale.

Used two flash guns to try to overcome the effects of the ND-grad on the closest stone.