and here's some in Millstone Grit - http://www.themodernantiquarian.com/post/16202 - which is the toughest species of sandstone. These have barely eroded since the day they were carved ...
Yay! I hoped you'd stick you head into this one Stonelifter :)
Howzit aal gannin?
I know you're adamant that these grooves are axe grinding artifacts. But the Devil's Arrows? How tall would you have to be to be using them to sharpen/grind an axe?