白垩系 bái'èxì Cretaceous System Origin Definitions Defs Strokes Stroke Words Sentences Sents 白垩 白堊 bái'è chalk chalk; a soft, white, porous limestone consisting mainly of calcium carbonate系 xì system (geology) (geology) a chronostratigraphic unit of rocks formed during a period of geological time, ranking below an erathem and above a series