Eyup Postie, It *is* the big rock chair. It's weird. From the side it looks like a half-disk buried halfway into the ground, but from the front, it looks like this.
The cairns are directly below this natural monolith, and the two stone circles either side may (heavy emphasis on the may) align onto the cleft between the monolith and the outcrop behind it. If you're ever up this way, gie's a shout. I've got a purpose built map showing where the interesting bits are. It's one of those spots that's right on the edge of two OS maps, which might be partly why the area gets bog all recognition, being overshadowed by that daft wall thing the romans built. I can waffle on for a good while about half baked theories of what may have been going on in this patch of the world :-)
D'oh, how slow of me not to put one and one together, a bit typical i'm afraid.
Ive got free reign for a few days next week, so anywhere within a five hour drive is in consideration, i've sadly neglected your patch of the world as I've only been up that way twice, so it's high on me list, but as ever its a long list.
Bloody romans !!