This put me in mind of the sight of that mineshaft, informally capped with lengths of old rail line, nestling close alongside one of the piers of the viaduct at Barrepta Cove.

Mark

Yes old mines used to measure themselves in fathoms. One I worked on, (1.5 miles down: 1320 fathoms)) spanned the metrication change-over, and the older production figures were quoted in square fathoms. I imagined this to be 6 foot by 6 foot, but no: it was a square yard! Three squared is not 3 + 3

Well done, both of you: I couldn't have coped with that - claustrophobia. 

Like TonyK, I never had to stoop so had no feeling of ill-ease on my job. I used to travel further to work than my father - and he travelled horizontally.

Invited down the father-in-law's coal mine, on the other hand, was a different kettle of fish. Slithering along the 2 foot high muddy stope like a serpent, I felt the weight of the mountain pressing upon my back - I think he had sent me to the thinnest coalseam on the pit!

I had to lie on my back in the warm slime and close my eyes - and breathe steadily - to regain my composure. If you drive a steam engine, think of the poor b****r digging your fuel!!

One of the mine captains gave me a requisition chit for "Oylskin jaquette", and another gave up on trying to spell "corrugated" and ordered "wiggly steel" instead. Either could look at a blank wall or rock at the end of a level in the mine and tell you instantly how long it would take to drill, how much explosive would be needed, how much rock would result and so on, and if I ever found myself stuck on Bodmin Moor in bad weather, I would rather have one of them with me than my accountant. Ask them about a square fathom, though, and my guess is they would use an obscure Cornish expression not usually heard in polite company, then get on with something else.

Thanks for the link to the photos. I was lucky enough to go on an underground tour of Geevor, though in sad circumstances as the mine was selling underground tours in an unsuccessful attempt to raise money to keep the pumps running. Much to see, and a strong sense, underground, of the warmth and the sense of space (plenty of headroom helped with that, and the rock was very competent, there was no sense of vast weights of strata needing to be handled carefully...)

Mark

I take it the source of this usage was the need to measure how much material had been mined, for estimating the amounts of useful ore and recovered metal, and also for workers' payments. For that, you multiply the width worked by the distance, and they might customarily both be in fathoms. To get a true volume you would multiply by the height of the working as well, but that's not going to vary so was left out. As it happens, for a lot of mines this height is about six feet! From the comments above that was so in Cornish mines, and I think in South Africa too. If you cut a greater height than that you just didn't get paid for doing it, but that's your problem.

While other meanings may have come in more recently, here's an older example. In reports of the flooding at Porkellis United Mines on 24th August 1858, I found the volume of water and "slime and refuse from the stamps" that entered the mine given in square fathoms. Here, a real volume is called for, and there is no obvious value of working height to assume. And the number given does look very like length x breadth x depth in fathoms.

If you want an even bigger puzzle, I have come across a few references to square cubic fathoms ...