Não informado. (2001). Bulletin of the Pennsylvania Geological Survey. Pennsylvania Geological Survey.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNão informado. Bulletin of the Pennsylvania Geological Survey. Harrisburg, Pa: Pennsylvania Geological Survey, 2001.
एमएलए (8वां संस्करण) प्रशस्ति पत्रNão informado. Bulletin of the Pennsylvania Geological Survey. Pennsylvania Geological Survey, 2001.
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