@inbook{NBERc6390,
 Crossref = "NBERking30-1",
 title = "XII. Factors Relating To Income From Mines, Quarries, and Oil Wells",
 author = "Willford Isbell King",
 BookTitle = "The National Income and Its Purchasing Power",
 Publisher = "NBER",
 pages = "315-325",
 year = "1930",
 URL = "http://www.nber.org/chapters/c6390",
}
@book{NBERking30-1,
 title = "The National Income and Its Purchasing Power",
 author = "Willford Isbell King",
 institution = "National Bureau of Economic Research",
 type = "Book",
 publisher = "NBER",
 year = "1930",
 URL = "http://www.nber.org/books/king30-1",
}