The minerals of Pennsylvania: Non-metallic minerals - Stone, Ralph W. (Ralph Walter), 1876-1964. (Harrisburg, Pa., Department of Internal Affairs, Topographic and Geologic Survey, 1939)
At head of title: Pennsylvania Geological survey, Fourth series
With Ashley, G. H. The undeveloped mineral resources of Pennsylvania. 1933. (Bulletin M18-A)
Bibliographical footnotes.
Keywords: Mines and mineral resources -- Pennsylvania