The OED points out that Colliers were makers and marketers of charcoal
before they were minders of coal.  (c1350 for the first use, 1594 for
the latter).
The OED doesn't refer to the exact phrase 'colliers pit', but it does
give a quote of 1573 for 'colliers hearth'.

Best wishes to all,

Pat

In message <[log in to unmask]>, Automatic digest processor
<[log in to unmask]> writes
> ...
>collier's pit.  I have found historical references to all but the last term.  It
>is also not a term used by USGS.  Does anyone know where it originated?
>
>Thanks
>JH Brothers IV

--
Pat Reynolds
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   "It might look a bit messy now, but just you come back in 500 years time"
   (T. Pratchett)