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Depths of the Earth: Caves and Caverns of the United States: Halliday, William R. , M. D.: 9780060023720: Amazon.com: Books
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Celebrated American Caverns, Especially Mammoth, Wyandot, and Luray Together with Historical, Scientific, and Descriptive Notices of Caves and Grottoes in Other Lands | Horace C. Hovey | First Edition
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