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An argillaceous limestone, which forms the basis of the oolitic formation.

A term originally applied to the thin-bedded limestone's occurring at the base of the oolitic system; in geol., that group or series of strata which in England immediately overlies the Trias or Upper New Red Sandstone; hydraulic cement made from calcareous nodules and bands of the lias strata.

n. An argillaceous lime-stone.