The middle one is the historically significant one on Brown Cow Hill. It is interesting the other 2 are almost equidistant apart on the same bearing (almost). I am not aware why. On a clear day they are also visible and not obscured by hills. It's tempting to think they were co-named by an O.S. suveyor who noticed these co-incidences. For the sake of completeness it is noted their is a fourth Clach elsewhere, very near the "Argyle Stone".