Many thanks to everybody who has helped me on this one. I have actually
managed to get on the moor and looked at Pigshill Droke and it turns out to
be a prehistoric reave (which was later used as a land boundary) which
tends to go against the consensus of a groove, cutting or valley. It also
turns out that the Pigshill was a 13th century farmstead called 'Pigswell'.
But once again, many thanks for all your helpful assistance.