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I found them maintaining their erect attitude, at points many miles apart, in beds both above and between the seams of coal. In order to explain this fact, we must suppose such shales and sandstones to have been gradually accumulated during the slow and repeated subsidence of the whole region. Triassic coal-shale, Richmond, Virginia. a. Estheria ovata. b. Young of same. c. Natural size of a. d.
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