Large archive of 1930s - 1950s potholing photos of fleabay.
http://www.ebay.co.uk/itm/CAVING-POTHOLING-Archive-145-photographs-30s-50s-superb-material-BRADFORD-/141780438602?hash=item2102c5ce4a
http://www.ebay.co.uk/itm/CAVING-POTHOLING-Archive-145-photographs-30s-50s-superb-material-BRADFORD-/141780438602?hash=item2102c5ce4a