I was commissioned to write a piece on County Durham for a magazine, not specifically anything to do with language, and I came across Pitmatic, the old language of the Durham miners. I say 'language' but it's a mixture of Durham dialect and specialised vocabulary, most of which, unsurprisingly,is technical and mining-related. Examples include: corf-batters (boys who scraped the coal out of filthy baskets), hoggers (shorts worn by miners underground), poss-tub (laundry items - soap, scrubbing brush etc) and arse-loop (a rope chair which miners sat on when repairing shafts).
People from County Durham are not technically Geordies (who are, strictly speaking, Tynesiders). They are termed Pit-yakkers, and Pitmatic is, or was, also known locally as Yakka. Pitmatic was originally called Pitmatical, which was a reference to both the pit (coalmine) and reminiscent of the word mathematical. Perhaps the idea was to stress the precision and scientific nature of the mining work.