ah if you came up that dastardly steep path from the aquaduct then you'd have gone straight past the well? - more of a spring with some stone round it really. Nice though. It's years since I've been and I never looked for the cairn at the time.
'Pattern of the Past' has loads of stuff relating to that area. He finds these little swirly patterns around all sorts of stones.. including ones that are blatantly along the side of the road to stop you bashing into the wall (probably). Which is a bit weird. But I like his diagrams.