1. Alberta Culture and Tourism, 2018. http://history.alberta.ca/energyheritage/coal/early-coal-history-to-1900/unearthing-ancient-mysteries/default.aspx (accessed March 2018).
2. Coal Energy Facts;American Coal Foundation,2018
3. Ancient Monuments, 2018. https://ancientmonuments.uk (accessed March 2018).
4. The Coal Business in Wyoming;Anderson,2014
5. Nature and Management of Tropical Peat Soils, Food and Agricultural Organization of the United Nations;Andriesse,1988