My ex has written a book on Wareside, and in her researches she found that the expression 'treacle miners' was often used for those who carted night-soil (human faeces) for use as a fertiliser. It's one of the best ways of enriching soil and from the 17th to 19th centuries, with the growth of towns but the inefficiency of the sewage systems, the night-soil carters were darned important. Not exactly fragrant, though!
The White Horse pub in Wareside has a cod history of the local treacle mines which is well worth a read - total nonsense, but very funny.