Note 10 — Chapter IV · MINERAL RESOURCES—SOME GENERAL QUANTITATIVE CONSIDERATIONS
Reading edition
Bastin, Edson S., and McCaskey, H. D., The work on mineral resources done by the U. S. Geological Survey: Min. Res. of the United States for 1918, U. S. Geol. Survey, pt. 1, 1920, p. 3a.