I don’t know if this has any bearing on the matter at all. But it’s interesting that Paulus says the stone was once “at the edge of an old stream”.
Hipping-Stones
Large stepping-stones in a brook. When passable by means of such stones, the water is said to be ‘hippinable’.
But then again, the next entry is:
Hippins
Children’s clothes; clouts. (North).
So stones for hopping across or doing your washing on, perhaps?
From the Dictionary of obsolete and provincial English, by Thomas Wright (1857) – which can be viewed on Google Books.
