I remember reading articles by Nellie Kirkham in "Mine and Quarry" in my student days
around 1950-52. I could afford to buy it then because the then owners had an offer - if you
started to subscribe while you were a student, you could have it for half price for life.
Sadly, a new company bought it some years later, and that offer was withdrawn!
Much as I admired and was interested in Nellie's articles, I think she may have been wrong
to say that while Derbyshire men sank square or rectangular shafts, Cornish men sank
oval ones.
As I recall the thinking, the shape of a shaft depended on the strength of the ground you
sank it through. Thus most coal mine shafts are circular, so you can line them with a ring
of brickwork or sections of cast iron cladding which, bolted together, made a circle. The cage
guides in these would be suspended steel ropes weighted at the bottom.
In hard rock which didn't need lining, on the other hand, square (or even better, rectangular)
shapes were the norm so they could be divided into compartment using a framework of
timber beams. In these, the cage guides would be vertical wooden beams.
I guess that in Cornwall, shafts which were mainly in granite would be rectangular (I seem
to remember that Robinson's shaft at South Crofty is this shape), while if it started in
weathered killas, and the ground was softer, a Cornish shaft might well start off oval, if it
needed a lining near the top.
Tony Brewis
|