Visited 16.05.09
“Billy Marshall’s Cave is situated at NX494679, approximately 900 metres north west of the summit. Again this cave is worth a visit, but difficult to find. Fortunately a rock above the cave has an iron bar protruding from it – thus helping to identify its location.”
The above quote is from Newton Stewart WalkFest.
It is more of a rock recess than a cave lying 2 metres below the slope and extending for around 10 metres. There is not much room for Billy Marshall’s Band of Gypsies.
Despite your cynicism that the cave goes back 10 miles and deep enough to singe a dog - I rejoice in your addition of photos.
I would be happy to be proved wrong if you can find your 10 mile cave.