Não informado. (1969). Pennsylvania Geology. Bureau of Topographic and Geologic Survey.
Chicago-viite (17. p.)Não informado. Pennsylvania Geology. Harrisburg, Pa: Bureau of Topographic and Geologic Survey, 1969.
MLA-viite (8. p.)Não informado. Pennsylvania Geology. Bureau of Topographic and Geologic Survey, 1969.
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