In reply to MG:
That's right, a chilling thought. Because one day (sooner rather than later in geological terms) it will fall down.
But I have huge problems with the geological time scale. My brain really can't do it, can't see the fantastically (million times?) speeded up image of what actually happened. I was thinking about this recently when I visited Black Rocks again: that the eastern gritstone edges were once part of a huge gentle dome that covered all the limestone scenery that you can see to the west. Yet Black Rocks is so hard, almost like granite - which is why mill wheels could be made from gritstone - that almost nothing, except in the minutest way, has changed on the crag for over a 100 years, as testified by many old B&W photos.