CHALK

a soft, pure white limestone composed of shells of microscopic marine animals, mostly Foraminifera, and rich in fo ils (corals, sponges, mollusca); geologically forms distinguishing feature of the Upper Cretaceous formation, being represented in England by the N. 8. Downs, York and Lincoln Wolds, Salisbury plain, Chiltern Hills; used for writing, preparation of lime, Rom. cement, putty.