Other then speculation that it may have been a nutting stone there is little evidence . It's actually a fairly common natural looking formation so in this case from the perception on this side of the fence the lack of evidence would suggest natural. The groove looks like a shaft abraider from far but lacks the smooth polished look one would expect from such.
I kind of like it though geofact nutting stone shaft abraider combo.
There are people trying to prove these are actually a form of ancient language, glyphs I think. Eoliths website is a guy in England who seems to know. A lot about this.
It looks like natural erosion on a rock. If you find one similar, it would definitely show a pattern. But again, context is everything, where it was found, etc.
It looks like natural erosion on a rock. If you find one similar, it would definitely show a pattern. But again, context is everything, where it was found, etc.