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Geological Reports of Pennsylvania, 1874—1884. | ||
P.—Coal Flora. N.—Levels. |
B, B², M, M², M³.—Chemical Analyses. O, O².—Catalogue of Specimens. |
Geological Reports of Pennsylvania, 1874—1884. | ||
P.—Coal Flora. N.—Levels. |
B, B², M, M², M³.—Chemical Analyses. O, O².—Catalogue of Specimens. |