Note 18 — Chapter VIII · THE ENERGY RESOURCES—COAL, OIL, GAS (AND ASPHALT)
Reading edition
Campbell, Marius R., The coal fields of the United States: Prof. Paper 100-A, U. S. Geol. Survey, 1917, pp. 5, 6, 7.
Reading edition
Campbell, Marius R., The coal fields of the United States: Prof. Paper 100-A, U. S. Geol. Survey, 1917, pp. 5, 6, 7.