The Primitive, or lower formations, supposed to have been formed in the chaotic state of the earth, because they have no trace of organized beings or petrifactions; they are chiefly composed of silicious and argillaceous earths, as granite, slate, &c.—Transition rocks, supposed to have been formed during the transition of the earth into a habitable state; they differ from the primitive, in containing the remains of marine animals:—the Secondary rocks, containing the remains of animals and vegetables, and consequently formed after their creation;—the Tertiary formation, composed of layers of clay, sand, gravel, and marl, and containing peculiar organic remains;—and the Alluvial formation, constituted of parts of previous rocks separated by water, &c., and deposited in beds.
Petrifaction, an animal or vegetable substance turned to stone.
Silicious, consisting of flint.
Transition, change from one state to another.
Argillaceous, clayey, consisting of clay.
Chaotic, resembling chaos, confused.
Chaos, confusion, a mingled heap; a term used in speaking of the world while yet without form; a Greek word, signifying a confused mass.
Alluvial, deposited from water.
Of what is this last compounded?
The Alluvial formation is composed of sand, gravel, loam, clay, turf, &c., and contains plants, roots, moss, bones, petrified wood, and skeletons of animals. It is distinguished from the Tertiary formation chiefly by its superior position, and by extending over regions where existing streams or other causes now in action could have produced it. Some geologists mention another formation called the Volcanic, because composed of minerals thrown from the crater of a volcano, such as pumice stones, lava, &c.