Among the specimens of Triassic rocks collected during the survey of the Fairfield and Gettysburg quadrangles, Pennsylvania, for folio publication, certain dark shales and hardened altered shales with molds of crystals were obtained, and were sent with specimens of metamorphosed sediments and igneous rocks to Prof. J. Volney Lewis for petrographic study. In a letter dated May 24, 1915, Professor Lewis wrote:

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