Another nice pic from Rhosyfelin -- thanks to Chris. He says this was taken about 40m upstream from the "quarry" -- presumably on the other side of the ridge, where the crags are "overhanging" and more precarious.
OK -- Chris wonders how crags as delicate as this can survive glaciation and assorted other destructive earth surface processes. Fair enough -- this is one of the great questions of glacial geomorphology. I won't pretend that I have an easy answer on tap. There are delicate crags all over the place, in areas which HAVE been glaciated quite recently. There are crags like this at Felin y Gigfran, at Nant y Bugail neat Trecwn, and in Tycanol Wood -- not to mention all those delicate crags up on the top of Preseli. In other places the crags are not so delicate -- they are smoothed off, and have obvious traces of glacial erosion on them. This is the classic beetling fragile precarious craggy rock in Pembrokeshire -- the Precambrian rhyolite crag at Maiden Castle, near Treffgarne: