In many parts of England certain small villages are jokingly said to have a secret treacle mine on their territory. 20th-century examples have been reported from Cumbria, Devon, Essex, Gloucestershire, Hampshire, Kent, Lancashire, Leicestershire, Norfolk, Surrey, Sussex, and Wiltshire; no doubt there are others too. Similar jokes are made about porridge or toothpaste quarries, snuff mills and jam mines, but they are less widespread and far less elaborate.
Basically, the joke is about impossibility—treacle is not found in mines, any more than money on trees—but it can work on many levels. Sometimes it is a taunt, implying that the people of X are such fools that they go digging for treacle, or too lazy to do honest work, or so poor they live only on bread and treacle; sometimes it is a hoax, in which a child or a newcomer is gulled or bewildered; sometimes a put-off from mother to child (‘Don't bother me now, I'm off to the treacle mine’); sometimes an emblem of local identity, proudly used in the name of a pub or a sports team, or as a tourist attraction.
The treacle mine is a theme on which poker-faced humorists play elaborate variations, the aim being to produce some plausible explanation of what and where it is, weaving in as many local allusions as possible. Perhaps the treacle comes from an abandoned dump of army food dating from the Crimean War (Chobham, Surrey); or by the geological compression of ancient sugar-cane forests (Dunchidoek, Devon); or it is waste oil from an American airbase (Tadley, Hampshire). The machinery for extracting it, and the docks from which it is exported, are lovingly described (Corpusty and Fring, Norfolk); one mine employs boggarts (Sabden, Lancashire).
Simpson, 1982; FLS News 18 (1993), 7–8; 19 (1994), 5–6; 20 (1994), 4–6; 21 (1995), 11–12;25 (1997), 12–13.