Paul Butler at Smallburn asked my advice as to what this is. I thought it was a thing that chickens would eat from. I know........daft but I've seen similar. Looks like Caithness stone. I know its not prehistoric so I'll remove the picture after a few days. Thanks in advance!
http://www.themodernantiquarian.com/site/12891/smallburn.html
The picture with the triangular stone.