4. The lower beds, placed under the vegetable, have received in geology the name of rocks, a word which in this acceptation implies not always the idea of a stony substance, but signifies a resting-place of some mineral substance. Some are formed of sand, of clay or loam, of chalk or pebbles; others of stones, properly speaking, of greater or lesser hardness, such as sand-stone, marbles, chalk, limestone, millstone, coals of the Earth, asphalt, etc. They say that the power of a rock depends upon its thickness.
By the inspection of the nature of these rocks or beds, one recognizes by certain signs, that they are produced by heated substances sometimes vitrified by the action of fire, others, by terrestrial substances deposited by water. Some of these substances have remained disintegrated, as sand; others at first in a pasty state, under the action of certain chemical agents or other causes, have become hardened, and have acquired in time the consistence of stone. Superposed stony beds show successive deposits. Fire and water have then played their parts in the formation of the materials composing the solid framework of the globe.