CHALK

of which the Downs and: | Dorset Heights, and so many of the io {} hills in England, consist, is a com: t | of calcium, carbon, and oxygen. Formed | ages ago at the bottom of the deep sea, of. | the shells of minute sea-creatares, it con- { | tains the fo ilised remains of many animals s| now extinct, and the proce by which it > | was formed is now going on at the bottem 8! of the ocean. By heating, carbonic acid gas?} is driven off from chalk, and we get lime. [s. 95]