687. The argillaceous trap, amygdaloid, clinkstone, several porphyries.
688. The talcose trap, basalt.
689. The calcareous trap, probably chalk.
d. Fire-formation.
VOLCANIC-ROCKS.
690. Volcanoes are secondary combustions of masses that have originated through the primary combustion, and are therefore only of local occurrence. Such combustible masses are without doubt bodies belonging to the class of Inflammables, and thus carbons, sulphur, sulphuretted metals. Simply burning gases would throw up on high the masses of earth, but not heat them to the degree of fusion.
691. By the heat of these combustions the masses of earth have been fused, forming lavas. The silicious lavas are obsidian, pitch-stone. The argillaceous lavas are the kinds usually met with. Next come the talcose lavas. The calcareous lavas are probably dolomite.
B.—METALLIC ORES AND INFLAMMABLES.
692. Metallic-ores and Inflammables are products of the planet, when completed, and have not originated along with the origin of the latter, like the earths. The question accordingly arises, what have been the forces by which the metals and Inflammables were produced.