Não informado. (1931). Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Mineral Industries. State College, Pa: Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Mineral Industries. Pennsylvania State College, College of Earth and Mineral Sciences, 1931.
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