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	1.	The Helderberg group from central Pennsylvania to southwestern Virginia, by Frank McKim Swartz ... by Swartz, Frank M. (Frank McKim), 1899- Series: Bulletin (Pennsylvania State University. Mineral Industries Experiment Station) ; no. 4 Material type: Text; Format: print ; Literary form: Not fiction Publication details: State College, Pa., School of mineral industries, 1929 Availability: No items available. Add to cart (remove)
	2.	The Devonian of Pennsylvania : Middle and upper Devonian / by Bradford Willard; Keyser limestone and Helderberg group, by Frank M. Swartz; Oriskany group, by Arthur B. Cleaves. by Pennsylvania. Bureau of Topographic and Geologic Survey Willard, Bradford, 1894- Swartz, Frank M. (Frank McKim), 1899- Cleaves, Arthur B. (Arthur Bailey), 1905- Series: Bulletin G ; 19 Material type: Text; Format: print ; Literary form: Not fiction Publication details: Harrisburg, Pa. : Dept. of internatl affairs, Topographic and geologic survey, 1939 Availability: No items available. Add to cart (remove)

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