http://www.worldcoal.org/coal/coal-mining/
http://www.rmcmi.org/education/coal-facts#.VWPkRc9VhBc
http://rogerphilpot.homestead.com/CoalEducation.html
http://www.wvminesafety.org/wvcoalfacts.htm
http://www.coal-miners-in-kentucky.com/CoalMiningFacts.html
http://www.worldcoal.org/coal/
http://www.wvcoalmining.com/coal-news/coal-mining-facts.html
http://www.dnr.state.mn.us/education/teachers/activities/soudan_mine/miningfacts.html
http://www.rmcmi.org/education/coal-facts#.VWPkRc9VhBc
http://rogerphilpot.homestead.com/CoalEducation.html
http://www.wvminesafety.org/wvcoalfacts.htm
http://www.coal-miners-in-kentucky.com/CoalMiningFacts.html
http://www.worldcoal.org/coal/
http://www.wvcoalmining.com/coal-news/coal-mining-facts.html
http://www.dnr.state.mn.us/education/teachers/activities/soudan_mine/miningfacts.html