I agree, except for one exception. Perhaps a byproduct of constructing
colliers pits to crack and remove limestone above coal was the creation of
charcoal production conical mounds as recreated at the Hopewell Village
Foundry Historic Site. Water, after the complete heating of the ground by the
charcoal production, would be poured to crack the limestone to get into the
coal bed. I seem to remember it being done and would have like to
investigated if it were done that way for the jasper quarries in eastern
Pennsylvania, near Vera Cruz and Macungie, PA, where there is a lot of
"karst" and limestone "sinkholes" some with water in them possibly abandoned
for that reason, the water impeding the excavation of the jasper
(cryptocrystalline quartz) for lithic production. The American Anthropologist
investigated the mines at the end of the last century and the famous Dr.
Mercer of Pennsylvania (The Mercer Folk Museum) used tree rings to date the
abandonment of the mines to about 1600 AD.

The "colliers pits" as applied to the maps of the Allegheny Portage Railroad
site may be then a bad example unless they can be explained as a twofold
process resulting in the pit from the charcoal production in karst
topography, perhaps. Then again it could be a useless term. However, it was
always impressed on me that the charcoal producer was the lowliest on the
scale of production in terms of wages and  benefits and if it was determined
that "colliers" produced charcoal and removed coal then the "pit" may have
been an unplanned or planned result and part of the specialization of labor
in iron production, the term later a loose term for "coal mine" after the
Industrial Revolution. My contact with the iron industry, (the numerous
reports on the Cold Spring Foundry, which indeed started with a pit of some
sort on site according to a very old map, enrelocatable, the pit, today)
shows that the language of foundry to be very unique and a "guild" of secrecy
with words exchanged with no usual meaning. Some of the more symbolic
language has been of course the "pig" iron after the flow released on the
sand floor from a "mother" pool into smaller pools, appearing to some
imaginations as sucklings, hence the supposed explanation of the name.
However, the other vocabulary defies interpretation, and history is left with
a list and no interpreter. This was for a foundry run in English, I imagine
others, (Wales, Scotland, etc.) to be equally perplexing.

In my own opinion,
George Myers