Cataclysm. A deluge. Etym., κατακλυζω, catacluzo, to deluge.
Cephalopoda. A class of molluscous animals, having their organs of motion arranged round their head. Etym., κεφαλη, cephale, head, and ποδα, poda, feet.
Cetacea. An order of vertebrated mammiferous animals inhabiting the sea. The whale, dolphin, and narwal are examples. Etym., cete, whale.
Chalcedony. A siliceous simple mineral, uncrystallized. Agates are partly composed of chalcedony.
Chalk. A white earthy limestone, the uppermost of the secondary series of strata.
Chert. A siliceous mineral, nearly allied to chalcedony and flint, but less homogeneous and simple in texture. A gradual passage from chert to limestone is not uncommon.
Chloritic Sand. Sand colored green by an admixture of the simple mineral chlorite. Etym., χλωρυς, chlorus, green.
Cleavage. Certain rocks, usually called Slate-rocks, may be cleaved into an indefinite number of thin laminæ which are parallel to each other, but which are generally not parallel to the planes of the true strata or layers of deposition. The planes of cleavage, therefore, are distinguishable from those of stratification.
Clinkstone, called also phonolite, a felspathic rock of the trap family, usually fissile. It is sonorous when struck with a hammer, whence its name.
Coal Formation. This term is generally understood to mean the same as the Coal Measures, or Carboniferous group.