There's something going on with the Popping stones. If you take a look at one of the pictures of the group together, looking upstream, then it's clear that the two lower rocks in front have been set into that position. This rock appears to have eroded microcups - http://www.themodernantiquarian.com/post/38478 - and we know this area was well populated in those times. There's plenty of monuments around Haltwhistle, a couple of miles to the east. Compare the 'demeanour' of these rocks with those of the circle on Haughton Common - http://www.themodernantiquarian.com/post/38478

But enough of this ! There's some Rock Art listed as being at Tortie, which is in this general vicinity. What is it ?