Most coalfields have one seam which, in that area, is thicker
than all the other seams, and often this seam is known by
some name such as "Main Coal".
Whereas most coal mines will have worked about six superimposed
seams at various times, my guess is that the main shaft of a mine
with "Main" in its title would have been sunk initially to the
horizon at which the Main Seam occurred, with a view to working
the thickest seam first.
Coal seam names can be quite local. For example, when I visited
Harworth Colliery in 1990, one of the seams it was working was
known as the "Top Hard/Dunsil". Elsewhere this seam is known as
the "Barnsley". Thus the "Main" in a mine's name, if indeed the mine
was named after a seam, as suggested above, was not necessarily
the same seam in different mines.
Tony Brewis
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