Campbell, Marius R., The coal fields of the United States: Prof. Paper 100-A, U. S. Geol. Survey, 1917, pp. 5, 6, 7.

Compiled from tables quoted by White, David, The petroleum resources of the world: Annals Am. Acad. Social and Political Sci., vol. 89, 1920, pp. 123 and 126.

White, David, loc. cit., p. 113.

See Arnold, Ralph, Petroleum resources of the United States: Econ. Geol., vol. 10, 1915, p. 707.

White, David, Late theories regarding the origin of oil: Bull. Geol. Soc. Am., vol. 28, 1917, p. 732.

McCoy, A. W., Notes on principles of oil accumulation: Jour. Geol., vol. 27, 1919, pp. 252-262.

White, David, Genetic problems affecting search for new oil regions: Mining and Metallurgy, Am. Inst. of Min. Engrs., No. 158, Sec. 21, Feb., 1920.

Mehl, M. G., Some factors in the geographic distribution of petroleum: Bull. Sci. Lab., Denison Univ., vol. 19, 1919, pp. 55-63.