I suppose it depends on how late in the 18th. Century we mean. By the 1780's the beginings of industrial infrastructure had begun but at that stage most power was still water, animal or human. Derby had moved to Coalbrookdale and had begun to use coke instead of charcoal by 1710 ( see
http://en.wikipedia.org/wiki/Coke_(fuel) ) and the Savery/Newcommen 'atmospheric engine' patent was granted in 1698
http://inventors.about.com/library/inventors/blsteamengine.htm . But there was only limited demand for coal until the middle of the 19th century, but when the growth came it was exponential with demand soaring in the 50 years between 1825 and 1875.
I'm aware that I haven't really given an answer and perhaps others on this forum can point to better sources of information but my feeling is that , at the turn of the 18th/19th century 100 men would be a large mine in any area of the country.
sleep is a caffeine deficiency.