Assuming I'm right, it's a short but very interesting pothole. At the foot of that shaft is a pool against the wall. The water normally flows off from the pool down a steep slope of cobbles (towards the photographer in the above shot) into the rest of the known pothole. The pool is a choked sump; I've been in it a body length or so. I always assumed it was an inlet sump.
But . . . on a trip in dry conditions a few years ago the water descending the 21 m shaft was cascading into that pool with nothing flowing down the cobble slope. This means that the pool is a downstream sump, perched curiously at the head of the slope. In uber-drought there's very little water sinking into it and as it's at the head of a slope it's a prime candidate for siphoning. If the sump could be dried up and then dug, who knows where it may lead? This pothole still holds many secrets . . . .
Always meant to have a play with this one but my projects list is so rammed I've never got around to it. If anyone else fancies a go, in drought, feel free. It's a fair way to the rising in Trollers Gill. Be good if you could P.M. me if you do have a go, so any findings can then be incorporated into the next Northern Sump Index.
But . . . was I right Skippy?