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144 same level. They are rarely twinned, almost always single, and occur over a large area irregularly distributed but with an average density of about 5 or 6 per 100 sq. ft. (10 ft. square). Exactly perpendicular to the true bedding. Where this is tilted, so are they. Always slightly and often very much harder than the surronding rock. Their material, sand, may be of about the same fineness as their matrix, but may also be somewhat coarser, with inclusions of small pebbles and possibly bone frags. (see sample, R). The sand in them shows no true bedding, but may have a vague zoning horizontally or nearly so of somewhat coarser and finer material, not corresponding to any structure in the matrix. Their apices are often more or less conical when little weathered. Like most of the harder ss. of the area, but unlike the matrix, weathering often turns the surface reddish. Below the conical apex they show some horizontal fluting, but p. 146.