Não informado. (1969). Pennsylvania Geology. Bureau of Topographic and Geologic Survey.
Chicagoスタイル(17版)引用形式Não informado. Pennsylvania Geology. Harrisburg, Pa: Bureau of Topographic and Geologic Survey, 1969.
MLA(8版)引用形式Não informado. Pennsylvania Geology. Bureau of Topographic and Geologic Survey, 1969.
警告: この引用は必ずしも正確ではありません.