In reply to UKC Logbooks:
Tilburthwaite is probably a miss spelling of Tilberthwaite.
The Foss Howe Boulders might better known as the Seathwaite Boulders in the Duddon valley.
Seathwaite Upper Slabs NY 228 124
Dufton Gill, These might be the sandstone quarries mentioned in the North of England Rock Climbs by Stew Wilson, 4 miles north of Appleby G.R. 688249
Post edited at 18:24