Cambrian.—The first or earliest period of the Paleozoic era of geologic time.
Cenozoic.—The present era of geologic time. It began at least several million years ago.
Chalk.—A soft, fine-grained, white limestone consisting mainly of tiny shells.
Conglomerate.—A sedimentary rock consisting of consolidated or cemented gravel. Often sandy.
Cretaceous.—The last period of the Mesozoic era of geologic time.
Crystal.—A regular polyhedral form, possessing a definite internal molecular structure, which is assumed by a substance in passing from the state of a liquid or gas to that of a solid. Nearly every mineral, under proper conditions, will crystallize.
Crystalline Rock.—A rock composed of closely fitting mineral crystals that have formed in the rock substance, as contrasted with one made up of cemented grains of sand or other materials, or with a volcanic glass.
Crystallography.—The study of crystals.
Devonian.—The middle one of the seven periods of the Paleozoic era of geologic time.
Dike.—A mass of igneous rock that has solidified in a fissure or crack in the earth’s crust.