Lifter of stones said
"In one of the pictures there is what-seems-to-be another stone, about a hundred yards away (probably it is just a tree)."
I briefly thought that as well, but it is a tree, unfortunatree

Dave

< Also the groove down one face of the menhir may have been carved in an act of symbolic art which we no longer understand ... >

...and if you check one of Josie's pikkies, you can see how people have been using one edge of the stone to sharpen knives on - or summat like that - sometime in the past. The small cuts or notches only occur on one particular edge.