I dunno either, but a pebble in OE is certainly "papolstan". BTW I have an unproved theory that some, possibly many, of our standing stones are Anglo-Saxon boundary, marker or ritual stones. Some may have had an earlier purpose as well of course.
They may have been erected as boundary markers originally. We don't know how old many of these land divisions are. The Halliwell long barrow is alongside the boundary of Halliwell and Smithills - there is a theory they were boundary markers too - suggesting that the same border was in place in the Neolithic Era.