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2. Twenhofel, W. H., "Treatise on Sedimentation" (2nd Edition. 1932), p. 680.
3. Lyell, Sir Charles, "On Fossil Rain-marks of the Recent, Triassic, and Carboniferous Periods", Quart. J. Geol. Soc. Lond., 7, 243 (1851).