Neptune?

Down at Ravenscar quite well hidden near the fault line lies this carved rock.  Its not particularly obvious and is quite large.  Its laid flat on the rocks and is far too heavy to stand up without using a lever of some sort.

From personal experience I'd guess that to do this carving would take a good few hours.  

Someone took a lot of time and effort to do this but I've never  been able to find out anything about it.

Any one know?

And here not far from the previous picture I came across another neptune, clearly by the same hand and yet again hidden away, in this case off the path down to the rocky foreshaw