I bet your right unclemac. I've never lived on a farm, but living a bit south of the Canadian shield I see erratic boulders in the strangest places. Probably why that was my first thought. Several years ago I found this near a marsh which has never been cultivated & assumed it an erratic but who knows? I know it's "Just a rock..." & the wrong forum for this, but whatever. Either way I agree that is likely natural USA1.