[37] Smith, George Otis, and others, The classification of the public lands: _Bull. 537, U.S. Geol. Survey_, 1913. [38] Schlumberger, C., _Study of underground electrical prospecting_: Translated from the French by Sherwin F. Kelly, Paris, 1920. Bergstrom, Gunnar, and Bergholm, Carl, "Teknisk Tidskrift, Kemi och Bergvetenskap," 1918, Book 12. [39] Hoover, Herbert C., _Principles of mining_: McGraw-Hill Book Co., New York, 1909, p. 32. [40] Leith, C. K., Use of geology in iron ore exploration: _Econ. Geol._, vol. 7, 1912, pp. 662-675. [41] Van Hise, C. R., and Leith, C. K., Geology of the Lake Superior region: _Mon. 52, U.S. Geol. Survey_, 1911. CHAPTER XV VALUATION AND TAXATION OF MINERAL RESOURCES POPULAR CONCEPTION OF MINERAL VALUATION The total returns from mining may not in the aggregate be far above the expenditure for exploration, development, and extraction; yet the total mineral wealth of the United States, on the basis of earning power and aside from the industries based on it, cannot be far from sixty billions of dollars, and this wealth has virtually come into existence since the 1849 gold rush to California. The mining industry supports a large population. These facts are the solid basis for the widespread popular interest in mineral investment--and mineral speculation. But there are other reasons for this interest,--the gambler's chance for quick returns, the "lure of gold," the possibility of "getting something for nothing," the mushroom nature of certain branches of the industry, the element of mystery related to nature's secrets, and the conception of minerals as bonanzas with ready-made value, merely awaiting discovery and requiring no effort to make them valuable. In the United States a factor contributing to the popular interest is the large freedom allowed by the laws to discover and acquire minerals on the public domain. Perhaps no other field of industry comes so near being common ground for all classes of people. The mineral industry is a field in which it is easy to capitalize not only honest and skillful endeavor, but hopes, guesses, and greed. It is not to be wondered at, therefore, that in the popular mind the valuation of a mineral resource is little more than a guess, and sometimes not even an honest one.